It wasnarrated that Ibn 'Abbas said:
"It was said: 'O Messenger ofAllah, why did you support (by supplicating for) those who shave(their heads) three times and those who cut (their hair) only once?'He said: 'Because they did not entertain any doubts.'" (DE)
English reference (DE): Vol. 4, Book 25, Hadith 3045 (DE)
Arabic reference (DE): Book 25, Hadith 3161 (DE)