Chapter on Fasting on the Day of Doubt
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 2|Chapter 16
سُئِلَ أَمِيرُ اَلْمُؤْمِنِينَ عَلَيْهِ اَلسَّلاَمُ: عَنِ اَلْيَوْمِ اَلْمَشْكُوكِ فِيهِ فَقَالَ «لَأَنْ أَصُومَ يَوْماً مِنْ شَعْبَانَ أَحَبُّ إِلَيَّ مِنْ أَنْ أُفْطِرَ يَوْماً مِنْ شَهْرِ رَمَضَانَ ».
Commander of the Faithful Imam Ali ibn Abi Talib عليه السلام was asked about the day of doubt (the day when it is uncertain whether it is the last day of Sha'ban or the first day of Month of Ramadan). Imam عليه السلام said: "Fasting one day from Sha'ban is more beloved to me than breaking my fast for one day in the Month of Ramadan."
- Ṣaḥīḥ al-Faqīh