Hadith: .

عَنْ أَبِي هُرَيْرَةَ رَضيَ اللهُ عنه قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ:
«مَنْ تَعَلَّمَ عِلْمًا مِمَّا يُبْتَغَى بِهِ وَجْهُ اللَّهِ عَزَّ وَجَلَّ لَا يَتَعَلَّمُهُ إِلَّا لِيُصِيبَ بِهِ عَرَضًا مِنَ الدُّنْيَا لَمْ يَجِدْ عَرْفَ الْجَنَّةِ يَوْمَ الْقِيَامَةِ» يَعْنِي رِيحَهَا.
[صحيح] - [رواه أبو داود وابن ماجه وأحمد] - [سنن أبي داود: 3664]

Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said:
"Whoever acquires knowledge that should be pursued for the sake of Allah Almighty for the sole purpose of securing worldly gains shall not smell the ‘Arf of Paradise on the Day of Judgment." i.e., its fragrance.
[Authentic hadith] - [Narrated by Abu Daoud & Ibn Majah & Ahmad] - [Sunan Abu Daoud - 3664]

Explanation

The Prophet (may Allah's peace and blessings be upon him) clarified that whoever learns religious knowledge—which is originally meant to seek the pleasure of Allah Almighty—but learns it only to attain worldly gain or benefit, such as wealth or status, will not smell the fragrance of Paradise on the Day of Judgment.

Benefits from the Hadith

1. The obligation of sincerity in seeking knowledge and encouraging this.
2. A stern warning against using religious knowledge for show off or as a means to attain worldly gain, as this is considered one of the major sins.
3. Whoever seeks knowledge for the sake of Allah and the worldly gains come to him as a result, it is permissible for him to take them, and it will not harm him.
4. As-Sindi said: His statement (the ‘Arf of Paradise) refers to its fragrance. This is an emphasis on the prohibition from Paradise, because whoever cannot even smell something certainly will not partake of it.
5. Whoever learns knowledge that is meant to be sought for the sake of Allah but does so for the sake of a job or other worldly aims must repent to Allah for that. And Allah will erase what resulted from the corrupt intention, for He is the Possessor of great bounty, Glorified and Exalted is He.
6. This warning is directed at the seeker of religious knowledge. As for someone who seeks knowledge of worldly sciences, such as engineering, chemistry, and the like, for the sake of worldly gain, then his intention is judged accordingly.