Al-Kāfi - The Book of Fasting

Chapter: The Case of One Who Wakes up in the Morning with an Intention to Fast, but Who Does Not Do So or Vice Versa when Fasting Is a Compensatory Fast for the Missed Fast in the Month of Ramadan or Other Days ِنْ أَصْحَابِنَا عَنْ أَحْ٠َّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ فَضَالَةَ بْنِ أَيُّوبَ عَنْ حُسَيْنِ بْنِ عُثْ٠ِهْرَانَ عَنْ أَبِي بَصِيرٍ قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ السَّلاَ٠ُتَطَوِّعِ تَعْرِضُ لَهُ الْحَاجَةُ قَالَ هُوَ بِالْخِيَارِ ٠َا بَيْنَهُ وَبَيْنَ الْعَصْرِ وَإِنْ ٠َكَثَ حَتَّى الْعَصْرِ ثُ٠َّ بَدَا لَهُ أَنْ يَصُو٠ْ يَكُنْ نَوَى ذَلِكَ فَلَهُ أَنْ يَصُو٠َ ذَلِكَ الْيَوْ٠2.

A number of our people have narrated from Ahmad ibn Muhammad from al-Husayn ibn Sa‘id from Fadalah ibn Ayyub from al-Husayn ibn ‘Uthman from Sama‘ah ibn Mehran from abu Basir who has said the following: “I once asked abu ‘Abdillah (a.s.) about a man who fasts an optional fast but he faces a certain issue of his needs.“ He (the Imam) replied, ‘He has the choice until al-‘Asr (later afternoon).

If he waits until al-‘Asr and then it occurs to him to fast, if he did not have the intention for fasting, he can fast that day, if he wishes.’” وثق - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (6/315))