My beloved friend instructed me to observe three things, the witr prayer before sleeping, the two units of the forenoon prayer, and fasting three days of every month.
حدثنا محمد قال حدثنا شعبة وأبو داود قال أخبرنا شعبة عن عباس يعني الجريري قال سمعت أبا عثمان يحدث
أوصاني خليلي بثلاث الوتر قبل النوم وركعتي الضحى وصوم ثلاثة أيام من كل شهر
Its isnad is sahih. It has occurred at 7138, and at 7180, 7503, 9189, and in more than thirty other places. It is found in the Six Books. Abu Uthman is Nahdi, named in the following hadith, and his name is Abdul-Rahman bin Mull.