"My beloved Prophet advised me to do three things which I will never give up, if Allah wills. He advised me to pray Duha, to pray Witr before sleeping, and to fast three days of each month." (Using translation from Nasāʾī 2404)
أَوْصَانِي خَلِيلِي ﷺ بِثَلَاثٍ لَا أَدَعُهُنَّ إِنْ شَاءَ اللهُ أَبَدًا أَوْصَانِي بِصَلَاةِ الضُّحَى وَبِالْوَتْرِ قَبْلَ النَّوْمِ وَبِصِيَامِ ثَلَاثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ