عَنْ صِلَةَ بْنِ زُفَرَ، قَالَ كُنَّا عِنْدَ عَمَّارِ بْنِ يَاسِرٍ فَأُتِيَ بِشَاةٍ مَصْلِيَّةٍ فَقَالَ كُلُوا . فَتَنَحَّى بَعْضُ الْقَوْمِ فَقَالَ إِنِّي صَائِمٌ . فَقَالَ عَمَّارٌ مَنْ صَامَ الْيَوْمَ الَّذِي يَشُكُّ فِيهِ النَّاسُ فَقَدْ عَصَى أَبَا الْقَاسِمِ صلى الله عليه وسلم.
Silah bin Zufar said:
“We were with Ammar bin Yasir when a roasted sheep was brought and he said: ‘Eat.’ Someone among the people said: ‘I am fasting.’ So Ammar said: ‘Whoever fasts on a day in which there is doubt, then he has disobeyed Abul-Qasim (ﷺ).”
Reported by Abu Dawud and others. Graded saheeh by Shaykh Albani rahimahullah
Note: Therefore, it is not permitted to fast on the day of doubt [i.e. 30th day of Sha’ban] unless it were to coincide with a day of fast which the person usually fasts on or a day which the person uses to make up for what was upon him of fast from last Ramadan and this is by the consensus of the scholars.
AbdulFattaah Bin Uthman