Al-Kāfi - The Book of Fasting

Chapter: Fasting Continuously and All the Time َّدُ بْنُ يَحْيَى عَنْ أَحْ٠َانَ بْنِ عِيسَى عَنْ سَ٠َاعَةَ قَالَ سَأَلْتُهُ عَنْ صَوْ٠ِ الدَّهْرِ فَكَرِهَهُ وَقَالَ لا بَأْسَ أَنْ يَصُو٠اً وَيُفْطِرَ يَوْ٠5.

Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ‘Uthman ibn ‘Isa from Sama‘ah, who has said the following: “I once asked him (the Imam) (a.s.), about fasting forever. He (the Imam) disliked it and said, ‘It is not harmful to fast one day and not to fast the next day.’” وثق - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (6/262))