Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) forbade ‘Uthmān ibn Mazh‘ūn to be celibate. If he had given him permission we would have castrated ourselves

عن سعد بن أبي وقاص رضي الله عنه قال: رد رسول الله صلى الله عليه وسلم على عثمان بن مظعون التَّبَتُّلَ، ولو أذن له لاختَصَيْنَا.
[صحيح] - [متفق عليه]

Sa‘d ibn Abi Waqqās (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) forbade ‘Uthmān ibn Mazh‘ūn to be celibate. If he had given him permission we would have castrated ourselves.
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Sa‘d ibn Abi Waqqās (may Allah be pleased with him) reported that ‘Uthmān ibn Mazh‘ūn had an extreme desire to commit himself to worship and abandon the pleasures of this life. He asked the Prophet (may Allah's peace and blessings be upon him) for permission to be celibate, i.e. refrain from marriage and dedicate himself to worshiping Allah. The Prophet (may Allah's peace and blessings be upon him) did not give him permission because abandoning the pleasures of this life and withdrawing from it to focus on worship alone is a form of extremism in religion and monasticism which are dispraised and objectionable in Islam. The correct religion is to perform the acts of worship that Allah has ordered us to perform while giving the bodily self its portion of the good things and pleasures of this life (in the proper and legal manner). Had the Prophet (may Allah's peace and blessings be upon him) given ‘Uthmān permission to be celibate many of diligent sincere worshipers would have followed him in adopting celibacy (to the extreme point of castration).