Hadith: Whoever acquires knowledge which should be pursued for the sake of Allah...

عن أبي هريرة رضي الله عنه أن النبي صلى الله عليه وسلم قال: «مَنْ تعلَّم علْمًا ممَّا يُبْتَغى به وَجْهُ الله عز وجل لا يَتَعلَّمُه إلا لِيُصِيبَ به عَرَضًا من الدنيا، لمْ يَجِدْ عَرْفَ الجنة يومَ القيامة».
[صحيح] - [رواه أبو داود وابن ماجه وأحمد]

Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Whoever acquires knowledge which should be pursued for the sake of Allah for the sole purpose of securing worldly gains shall not smell the fragrance of Paradise on the Day of Judgment."
Sahih/Authentic. - [Ibn Maajah]

Explanation

This Hadīth points out that if a person seeks one of the spheres of knowledge that are usually pursued for the sake of Allah – and these are the Shar‘i sciences and the supporting disciplines of the Arabic language and such – and only aims at worldly gains, like money or prestige, by doing this, and he does not seek the pleasure of Allah and the Hereafter, then Allah, the Almighty, will punish him by depriving him of the smell of Paradise. This is because he pursues the worldly life by doing the very acts intended for the Hereafter. His deprivation of the smell of Paradise is an overstatement signifying that Paradise shall be strictly forbidden for him, since a person who is not allowed to smell something would surely not be permitted to get it. However, this is taken to mean that he does not deserve to enter Paradise. After all, a sinner's fate is left to be decided by Allah, the Almighty, if he dies as a believer.