ʿUyūn akhbār al-Riḍā
Hadith 103103 - وَبِهذَا الإِسنادِ قالَ: قالَ عَلِىُّ بْنِ أَبِي طالِبٍعَلَيْهِ السَّلامُ: لا اعتِكافَ إِلاّ بِالصَّومِ.
31-103 According to the same documentation, Ali ibn Abi Talib (a.s.) said, “No one can go into seclusion in the mosque without fasting.”