The Signs of Non-Beneficial Knowledge:
An indicative sign of this non-beneficial knowledge is that it breeds haughtiness, pride and arrogance in the one who possesses it. And it causes him to seek after grandeur and elevation in the worldly life and to compete for that. It also leads one to pursue competing with the scholars, arguing with the foolish and turning the people’s attention his way. And it has been reported that the Prophet (صلى الله عليه و سلم) said that whoever seeks knowledge for these reasons, then “the Fire, the Fire.” 
It could be that some of the people who possess these types of knowledge claim to know Allaah, seek after Him and abstain from everything apart from that, however, their goal behind that is for nothing else but to gain a high place in certain people’s hearts, such as that of the rulers and their likes. Perhaps their goal is to have these people think good thoughts about them or to gain large gatherings of followers or to have them venerate them because of that.
Another sign of this is when one openly claims to have a close relationship with Allaah, i.e. claims to be a walee, as the People of the Scripture would do, and as the Qaraamitah, Baatiniyyah and their likes would assert for themselves.
This is contrary to what the Salaf were upon for they would constantly belittle and scorn themselves, in hidden and in open. ‘Umar said: “Whoever says he is knowledgeable is really ignorant. And whoever says he is a believer is really a disbeliever. And whoever says he is in Paradise is in the Hellfire.”
Also from its signs is that one fails to accept and submit to the truth, and that he acts arrogantly towards those who speak the truth, especially if that person is considered below them in the eyes of the people. Also from its signs is that one persists upon falsehood out of fear that the people’s hearts will turn away from him if he openly shows his going back to the truth.
Perhaps these individuals may even openly condemn and belittle themselves with their tongues in front of large gatherings so that people will believe that they are truly humble, thus drawing (their) praises for that. And this is from the most intricate and subtle forms of showing off (riyaa), as indicated by the Taabi’een and the scholars that came after them. Furthermore, their blatant acceptance and receipt of such praise is to such an extent that it negates any honesty or sincerity on their part. This is since a truly honest person fears hypocrisy for himself and dreads the thought of having a bad end, whereas these individuals busy themselves with accepting and consenting to praises.
So based on this, one of the signs that people have beneficial knowledge is that they don’t see themselves as having any special position or status, and that they hate with their hearts any commendation or praise and that they do not exalt themselves arrogantly over anyone.
Al-Hasan said: “The Faqeeh (one with understanding of the Religion) is only he who abstains from the worldly life, longs for the next life, has deep insight into his Religion and is persistent in worshipping his Lord.” 
In another narration, he said: “He is one who does not envy those above him, nor does he belittle those below him, nor does he charge any fee for the knowledge that Allaah has given him.”
A statement with a similar meaning to this last one was reported on Ibn ‘Umar as a saying of his. So every time the people who have beneficial knowledge increase in this type of knowledge, they increase in humbleness, fear, lowliness and submission to Allaah.
One of the Salaf said: “A person with knowledge should place dirt upon his head out of humbleness to his Lord.” 
For indeed every time he increases in knowledge and awareness of his Lord, He increases in fear and love for Him as well as submission and debasement towards Him.
The Signs of Beneficial Knowledge:
From the signs that one has beneficial knowledge is that it leads him to flee from the worldly life and its splendors, as well as from leadership, fame and praise. Keeping far away from these things and exerting one’s efforts in avoiding them are indications that one has beneficial knowledge. And if he were to fall into committing any of these things unintentionally and unwillingly, he would be in immense fear of being punished for that since he would fear that such (praise or leadership or fame) is perhaps a plot or gradual delusion (before inevitable punishment from Allaah). Such was the case with Imaam Ahmad, for he would fear for himself when his name became famous and his reputation spread.
Also from the signs of beneficial knowledge is that one does not claim to have knowledge nor does he use it to act arrogantly towards anyone, nor does he describe anyone as being ignorant – except for those who oppose the Sunnah and its followers, for in this case, he may speak about them out of anger for the sake of Allaah and not his own sake nor intending to elevate himself over anyone.
As for the one who does not have beneficial knowledge, his only concern is to use his knowledge to arrogantly elevate himself over people and to manifest the virtue of his knowledge to them while at the same time ascribing them to ignorance. His only concern is to belittle them so that he may exalt himself over them by doing that. This is one of the vilest and most despicable of actions. Perhaps he may even describe those scholars that came before him as being ignorant, negligent and forgetful. So his love for himself and his love for exposing himself leads him to think highly of himself while thinking poorly of those who preceded him!
Those who possess beneficial knowledge are upon the opposite of this, for they think poorly of themselves while thinking highly of those scholars that came before them. And they affirm with their hearts and souls the virtue and superiority that their predecessors have over them and their own inability to reach and attain the levels that they were at, let alone get near to them.
How beautiful was the response of Imaam Abu Haneefah when he was asked about ‘Alqamah and Aswad as to which of them was better. He replied saying: “By Allaah, we are not qualified to even mention their names, so how can we choose between them?”
When the etiquettes of those who preceded would be mentioned, Ibn Al-Mubaarak would recite the following verses of poetry:
“Do not present our mention along with their mention,
The healthy one who walks is not like the crippled.”
So if this individual with non-beneficial knowledge feels that he is superior to those who came before him in terms of producing elaborate speech and statements, he will then assume that he is also superior to them in knowledge and rank before Allaah, due to his having a special virtue over those who preceded him. This will then lead him to scorn those who came before him (i.e. the Salaf) and audaciously accuse them of having little knowledge. However, this ignoramus doesn’t realize that the reason why the Salaf made such few statements was only because of their piety and fear of Allaah. Had they wanted to speak profusely and elaborate themselves through many statements, they would not have been unable to do it.
 Saheeh: Reported by Ibn Maajah (254) from the narration of Jaabir bin ‘Abdillaah and authenticated by Al-Albaanee in Saheeh-ul-Jaami’ (7370).
 Al-Qaraamitah: They are one of the deviant factions that emerged from the Raafidah whose adherents follow Abu Sa’eed Bahraam Al-Hanaabee who was the founder of the Qaraamitee belief. They believed that ‘Abdullaah bin Al-Haarith Al-Kandee was a prophet and so would worship him. And they have other corrupt beliefs apart from that.
 Al-Baatiniyyah: This is a name given to a group that splintered from the Isma’eeli Shiites. They believe that the entire Book of Allaah is open to reinterpretation and claim that it cannot be understood in its apparent (literal) form and so as a result they went astray. Their beliefs have influenced the Sufi movement, which claims that all of the Qur’aan has an apparent as well as a hidden meaning.
 Reported by Ahmad in az-Zuhd (pg. 267), Ad-Daarimee (1/89), Al-Aajurree in Akhlaaq-ul-‘Ulamaa (pg. 74), and Abu Nu’aim in Hilyat-ul-Awliyaa (2/147) and its chain of narration is sound (hasan). [A]
 Reported by Ad-Daarimee (1/88) as a statement of Ibn ‘Umar. [A]
 Reported by Al-Aajurree in Akhlaaq-ul-‘Ulamaa (pg. 71 and Al-Khateeb in al-Faqeeh wal-Mutafaqqih (2/113) as a statement of Ayoob, and its chain of narration is authentic (saheeh). [A]
 He was the great Imaam, Abu Haneefah An-Nu’maan bin Thaabit, the Jurist from Iraq. He saw Anas bin Maalik on more than one occasion. He was pious, knowledgeable and diligent in performing deeds. Ash-Shaafi’ee said about him: “With regards to Fiqh, the people are dependent upon Abu Haneefah.” He died in 150H.
 He was ‘Alqamah bin Qais bin ‘Abdillaah bin Maalik bin ‘Alqamah An-Nakha’ee from Koofah, Iraq. He was born during the lifetime of Allaah’s Messenger but never met him. He was from the major Taabi’een, being the main Jurist and Muhaddith of the people of Iraq. He studied very closely under Ibn Mas’ood and spread his knowledge after him, passing rulings and verdicts. He died in 72H and some say in 73H.
 He was Al-Aswad bin Yazeed bin Qais An-Nakha’ee from the companions of Ibn Mas’oodt. His kunyah was Abu ‘Amr, but he was also called Abu ‘Abdir-Rahmaan. He was from the major Taabi’een, reliable and knowledgeable, and he narrated many hadeeth. He passed away in either 74H or 75H.
Imam Ibn Rajab Al-Hanbalee, may Allah have mercy upon him
Source: Fadlu ‘Ilm-is-Salaf ‘alaa ‘Ilm-il-Khalaf (pg. 39-43, Dar-ul-Imam Ahmad Ed.). Translation taken from http://www.al-ibaanah.com (offline).