رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 144
The Book of Miscellany
Moderation in Worship
وَعَنِ ابْنِ مَسْعُودٍ رَضِيَ اللَّهُ عَنْهُ أَنَّ النَّبِيِّ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ قَالَ: "هَلَكَ الْمُتَنَطِّعُونَ" قَالَهَا ثَلاَثًا " ((رَوَاهُ مُسْلِم))
Ibn Mas'ud (May Allah be pleased with him) reported: The Prophet (ﷺ) said, "Ruined are those who insist on hardship in matters of the Faith." He repeated this three times. [Muslim]
Riyad as-Salihin, 144