Mishkat al-Masabih
Mishkat al-Masabih 181
وَعَن أَنَسِ بْنِ مَالِكٍ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ يَقُولُ: لَا تُشَدِّدُوا عَلَى أَنْفُسِكُمْ فَيُشَدِّدَ اللَّهُ عَلَيْكُمْ فَإِنَّ قَوْمًا شَدَّدُوا عَلَى أَنْفُسِهِمْ فَشَدَّدَ اللَّهُ عَلَيْهِمْ فَتِلْكَ بَقَايَاهُمْ فِي الصَّوَامِعِ والديار (رَهْبَانِيَّة ابتدعوها مَا كتبناها عَلَيْهِم) رَوَاهُ أَبُو دَاوُد
Anas ibn Mālik reported that the Messenger of God used to say: ‘Do not impose hardship on yourselves, or God will impose hardship on you. Some people imposed hardship on themselves, and God imposed hardship on them; their remnants are those in hermitages and monasteries.’ He then recited: ‘Monasticism they invented; We did not prescribe it for them.’ (Qur’an 57:27.) Abū Dāwūd transmitted it.