Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Nafi‘ that when Hazrat Abdullah bin Umar (may Allah be pleased with them) would ascend Safa, he would face the Ka‘bah, then recite takbeer three times, and then recite this supplication: La ilaha illallahu wahdahu la sharika lahu, lahul mulku wa lahul hamdu, wa huwa ‘ala kulli shay’in qadeer, raising his voice, and then make a brief supplication. Then he would do the same at Marwah, until in seven rounds he would do this seven times, thus making twenty-one takbeers. He would not even be close to finishing when we would already be tired, even though we were young.