Ubaydullah bin 'Abdullah bin 'Utba عبيد الله بن عبد الله بن عتبة بن مسعود · The Book of Fasting

a Bedouin came to the Messenger of Allah with unkempt hair and said: "O Allah has enjoined upon me of Salah." He said: "The five daily prayers, unless you do any more voluntarily." He said: "Tell me what Allah has enjoined upon me voluntarily." He said: "Tell me what Allah has enjoined upon me of fasting." He said: "Fasting the month of Ramadan, unless you do any more voluntarily." He said: "Tell me what Allah has enjoined upon me of…

"If you wish then fast and if you wish then do not fast."