"I heard Abu Dharr, at Ar-Rabadhah, saying: 'The Messenger of Allah said: if you want to fast at any time during the monthm then fast on the thirteenth, fourteenth and fifteenth."'
لِي رَسُولُ اللَّهِ ﷺ إِذَا صُمْتَ شَيْئًا مِنَ الشَّهْرِ فَصُمْ ثَلاَثَ عَشْرَةَ وَأَرْبَعَ عَشْرَةَ وَخَمْسَ عَشْرَةَ