In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Imaam Ibn Rajab [rahimahullaah] said: All praises and thanks be to Allaah, the Lord of Aalameen [mankind, jinns and all that exists]. And may Allaah exalt and grant Muhammad a lot of peace, his family and Sahaabah. To proceed:

These are brief statements regarding the meaning of knowledge and its categorization into ‘Beneficial knowledge’, ‘Unbeneficial knowledge’, Blameworthy knowledge’ and a notification regarding the virtue of the knowledge of the Salaf [i.e. the pious predecessors] over the knowledge of the khalaf [i.e. those who came after the Salaf]. Therefore, I say- and Allaah’s aid is sought, I place my trust in Him and there is neither strength nor power except with Allaah.

The Meaning of Knowledge and Its Categorisation

Indeed, Allaah mentioned-sometimes- knowledge in His Book with praise and that is [in reference to] ‘Beneficial Knowledge’.  And at other times, He mentioned knowledge with dispraise and that is [in reference to] ‘Unbeneficial knowledge’. As for the first type [i.e. Beneficial Knowledge], then its example is mentioned in the statement of Allaah [The Most High]: [قُلۡ هَلۡ يَسۡتَوِى ٱلَّذِينَ يَعۡلَمُونَ- Are those who know equal to those who know not?] [39:9]

And the statement of Allaah [The Most High]: [شَهِدَ ٱللَّهُ أَنَّهُ ۥ لَآ إِلَـٰهَ إِلَّا هُوَ وَٱلۡمَلَـٰٓٮِٕكَةُ وَأُوْلُواْ ٱلۡعِلۡمِ   – Allah bears witness that La ilaha illa Huwa (none has the right to be worshipped but He), and the angels, and those having knowledge (also give this witness)] [3:18]

And the statement of Allaah [The Most High]: [وَقُل رَّبِّ زِدۡنِى عِلۡمً۬ا   -And say: “My Lord! Increase me in knowledge]. [20:114]

And the statement of Allaah [The Most High]: [إِنَّمَا يَخۡشَى ٱللَّهَ مِنۡ عِبَادِهِ ٱلۡعُلَمَـٰٓؤُاْۗ – It is only those who have knowledge among His slaves that fear Allah]. [35:28]

And what Allaah has stated regarding the story of Aadam- when Aadam was taught the names of those things and were then presented to the Angels, so the Angels – [as Allaah informed us] – said: [سُبۡحَـٰنَكَ لَا عِلۡمَ لَنَآ إِلَّا مَا عَلَّمۡتَنَآ‌ۖ إِنَّكَ أَنتَ ٱلۡعَلِيمُ ٱلۡحَكِيمُ – Glory be to You, we have no knowledge except what you have taught us]. [2:32]

And what Allaah [The Most High] has stated regarding the story of Moosaa [alayhis-salaam] and Khidr- that Moosaa said to him: [هَلۡ أَتَّبِعُكَ عَلَىٰٓ أَن تُعَلِّمَنِ مِمَّا عُلِّمۡتَ رُشۡدً۬ا – “May I follow you so that you teach me something of that knowledge (guidance and true path) which you have been taught (by Allah)?”] [18: 66]

This is beneficial knowledge.

Indeed, [we] have been told about a people who were given knowledge but their knowledge did not benefit them; for even though this [knowledge] is actually ‘Beneficial Knowledge’, however its possessor was not benefited by it. Allaah [The Most High] said: [مَثَلُ ٱلَّذِينَ حُمِّلُواْ ٱلتَّوۡرَٮٰةَ ثُمَّ لَمۡ يَحۡمِلُوهَا كَمَثَلِ ٱلۡحِمَارِ يَحۡمِلُ أَسۡفَارَۢا‌ۚ  – The likeness of those who were entrusted with the (obligation of the) Taurat (Torah) (i.e. to obey its commandments and to practise its legal laws), but who subsequently failed in those (obligations), is as the likeness of a donkey who carries huge burdens of books (but understands nothing from them). [Surah Al-Jumu’ah Ayah 5]

Allaah [The Most High] said: [وَٱتۡلُ عَلَيۡهِمۡ نَبَأَ ٱلَّذِىٓ ءَاتَيۡنَـٰهُ ءَايَـٰتِنَا فَٱنسَلَخَ مِنۡهَا فَأَتۡبَعَهُ ٱلشَّيۡطَـٰنُ فَكَانَ مِنَ ٱلۡغَاوِينَ  – And recite (O Muhammad ) to them the story of him to whom We gave Our Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.), but he threw them away, so Shaitan (Satan) followed him up, and he became of those who went astray….up to the statement of Allaah: [وَٱتَّبَعَ هَوَٮٰهُ‌ۚ   – and followed his own vain desire] [Surah Al-A’raaf Aayaat 175-176]

And Allaah [The Most High] said: [فَخَلَفَ مِنۢ بَعۡدِهِمۡ خَلۡفٌ۬ وَرِثُواْ ٱلۡكِتَـٰبَ يَأۡخُذُونَ عَرَضَ هَـٰذَا ٱلۡأَدۡنَىٰ  – Then after them succeeded an (evil) generation, which inherited the Book, but they chose (for themselves) the goods of this low life (evil pleasures of this world)…[up to the statement of Allaah]: وَدَرَسُواْ مَا فِيهِ‌ۗ And they have studied what is in it (the Book). [Surah Al-Araaf Aayaat 169-170]

As for the knowledge which Allaah [The Most High] mentioned by way of dispraise, it is that which He [The Most High] mentioned regarding magic:

وَيَتَعَلَّمُونَ مَا يَضُرُّهُمۡ وَلَا يَنفَعُهُمۡ‌ۚ وَلَقَدۡ عَلِمُواْ لَمَنِ ٱشۡتَرَٮٰهُ مَا لَهُ ۥ فِى ٱلۡأَخِرَةِ مِنۡ خَلَـٰقٍ۬‌ۚ

And they learn that which harms them and profits them not. And indeed they knew that the buyers of it (magic) would have no share in the Hereafter. [2:102]

And the statement of Allaah [The Most High]:

فَلَمَّا جَآءَتۡهُمۡ رُسُلُهُم بِٱلۡبَيِّنَـٰتِ فَرِحُواْ بِمَا عِندَهُم مِّنَ ٱلۡعِلۡمِ وَحَاقَ بِهِم مَّا كَانُواْ بِهِۦ يَسۡتَہۡزِءُونَ

Then when their Messengers came to them with clear proofs, they were glad (and proud) with that which they had of the knowledge (of worldly things): And that at which they used to mock, surrounded them (i.e. the punishment). [40:83]

And the statement of Allaah [The Most High] said:

يَعۡلَمُونَ ظَـٰهِرً۬ا مِّنَ ٱلۡحَيَوٰةِ ٱلدُّنۡيَا وَهُمۡ عَنِ ٱلۡأَخِرَةِ هُمۡ غَـٰفِلُونَ

They know only the outside appearance of the life of the world (i.e. the matters of their livelihood, like irrigating or sowing or reaping, etc.), and they are heedless of the Hereafter. [30:7]

Likewise, the Sunnah categorises knowledge into ‘Beneficial Knowledge ‘ and ‘Unbeneficial Knowledge’, and that [one should] seek refuge with Allaah from ‘Unbeneficial knowledge’ and to ask Allaah for ‘Beneficial Knowledge’. Imaam Muslim [rahimahullaah] reports from Zaid Ibn Arqam [radiyallaahu-anhu] that the Prophet [sallal-laahu-alayhi-wasallam] used to say:

اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنْ عِلْمٍ لَا يَنْفَعُ وَمِنْ قَلْبٍ لَا يَخْشَعُ وَمِنْ نَفْسٍ ‏لَا تَشْبَعُ ‏ ‏وَمِنْ دَعْوَةٍ لَا يُسْتَجَابُ لَهَا

O Allaah! I seek refuge with You from knowledge that does not benefit; from a heart that fears not; from a soul that does not become satisfied and a supplication that is not answered. [Muslim 2722]

[Fadl Ilm As-Salaf Alaa Ilm Al-Khalaf’ pages 42-45. Slightly paraphrased]