" I heard the Messenger of Allah say: 'The month of patience ( Ramadan) and three days of each month is fasting for a lifetime."' (Sahih). (Using translation from Nasāʾī 2408)
سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ «شَهْرُ الصَّبْرِ وَثَلَاثَةُ أَيَّامٍ مِنْ كُلِّ شَهْرٍ صَوْمُ الدَّهْرِ»