Musannaf Ibn Abi Shaybah

Hazrat Nafi’ reports that Hazrat Ibn Umar (may Allah be pleased with them both) when he would ascend the Safa hill, he would face the Ka’bah, then say takbeer three times, then recite these words: There is no deity except Allah, He is alone, He has no partner, His is the dominion and for Him is all praise, and He is powerful over everything, and he would raise his voice with these words. Then he would supplicate for a while, then do the same on the Marwah hill, continuing in this manner for seven rounds, so that the number of takbeers would become twenty-one. Even though we were young, we would become very tired near the end.