Yahya related to me from Malik from Ibn Shihab from Ubaydullahibn Abdullah ibn Utba ibn Masud from Abdullah ibn Abbas that theMessenger of Allah, may Allah bless him and grant him peace, left forMakka in Ramadan during the year of the conquest, and fasted until hereached al-Kadid. He then broke the fast, and so everyone else did soas well. What people used to do was act according to whatever theMessenger of Allah, may Allah bless him and grant him peace, had donemost recently.
USC-MSA web (English) reference: Book 18, Hadith 21
Arabic reference: Book 18, Hadith 655