Abu Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah (peace be upon him) said: "The example of a person who learns knowledge then does not teach it is like the one accumulates money, but does not spend out of it." (1)
Explanation of the Hadith:
Al Munawy said: As for the Prophet's saying: "The example of a person who learns knowledge then does not teach it is like the one who accumulates money, but does not spend out of it," Knowledge and money in this case will be against their owners on the Day of Recompense. So, a scholar has to teach his knowledge to the people for the sake of Allah (may He be Exalted) and should not show off while teaching them even if they are in dire need to his knowledge, but should attribute favor to them because they controlled their hearts to draw near Allah by obtaining knowledge. Their example is like the one who rents a land to cultivate it, so he benefits himself and benefits others, and except for a learner, a teacher will not gain reward. (2)
Lessons gained from the Hadith:
1- It is not permissible for a scholar to conceal knowledge to which the people need. Allah (may He be Exalted) says: "Verily, those who conceal the clear proofs, evidences and the guidance, which We have sent down, after We have made it clear for the people in the Book, they are the ones cursed by Allâh and cursed by the cursers." [Surat Al Baqarah: 159].
2- Withholding knowledge is the cause for the circulation of ignorance, and spreading of heresies, bad manners, forbidden relationships, and other types of sins.
3- The one whom Allah granted knowledge should exert more efforts to teach it to the people for the sake of Allah (may He be Exalted) and for benefitting the people in terms of their worldly affairs and religion in order to gain the blessings in the world and the great reward in the Hereafter. Moreover, the one whom Allah granted money should spend it on himself, his needy Muslim brothers, and in the cause of Allah so that money would not turn against him in the worldly life and in the Hereafter.
(1) Al Mu`jam Al Awsat of At-tabarany, 1/394, No. (693)
and Haythamy in Al Majma`, 1/164. Al Albany graded it as authentic, see: As-Silsilah As-Sahihah, No. (3479).
(2) Faydul-Qadir of Al Munawy, 5/ 510.