What was the instruction that the Prophet Muhammad (saw) gave Abu Murra which he vowed to never abandon?
 Abu Murra, the freed slave of Umm Hani, narrated on the authority of Abu Darda':                      My Friend (may peace be upon him) instructed me in three (acts), and I would never abandon them as long as I live. (And these three things are): Three fasts during every month, the forenoon prayer, and this that I should not sleep till I have observed the Witr prayer.