'Abdullah bin Mas'ud Radiyallahu 'Anhu reports:
"Rasulullah Sallallahu 'Alayhi Wasallam fasted for three days at the beginning of every month, and he very seldom did not fast on Friday". (RU)
English reference (RU): Book 42, Hadith 286 (RU)
Arabic reference (RU): Book 43, Hadith 303 (RU)