Source Of Sunnah
Some rituals were already there in the Arab society, uncorrupted, coming right from the Prophet Ibrahim, as his tradition, some sunnah was taught by Jibrail, especially the prayer and its timings. For example see the following hadith: Narrated Abdullah Ibn Abbas: The Messenger of Allah صلی اللہ علیہ وسلم said: Gabriel صلی اللہ علیہ وسلم led me in prayer at the House (i. e. the Kabah). He prayed the noon prayer with me when the sun had passed the meridian to the extent of the thong of a sandal; he prayed the afternoon prayer with me when the shadow of everything was as long as itself; he prayed the sunset prayer with me when one who is fasting breaks the fast; he prayed the night prayer with me when the twilight had ended; and he prayed the dawn prayer with me when food and drink become forbidden to one who is keeping the fast. On the following day he prayed the noon prayer with me when his shadow was as long as himself; he prayed the afternoon prayer with me when his shadow was twice as long as himself; he prayed the sunset prayer at the time when one who is fasting breaks the fast; he prayed the night prayer with me when about the third of the night had passed; and he prayed the dawn prayer with me when there was a fair amount of light. Then turning to me he said: Muhammad, this is the time observed by the prophets before you, and the time is anywhere between two times. (Abu Daud, 393)