عَنْ عُثْمَانَ بْنِ أَبِي الْعَاصِ الثَّقَفِيِّ رَضِيَ اللَّهُ عَنْهُ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ يَقُولُ: ((صِيَامٌ حَسَنٌ: صِيَامُ ثَلَاثَةِ أَيَّامٍ مِنَ الشَّهْرِ))
It is narrated from Sayyiduna Uthman bin Abi Al-Aas Thaqafi (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Fasting three days in every month is the best of fasts.