Ibn Jurayj (may Allah have mercy on him) said: I said to Nafi' (may Allah have mercy on him): "Is there any saying that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to hold to?" He said: "Do not ask about that; it is not obligatory." But I did not leave him until he told me. He said: "He used to stand for a very long time, so much so that, were it not for our shyness before him, we would have sat down. He would say the takbir 'Allahu akbar' (Allah is the Greatest) three times, then say: 'La ilaha illallahu wahdahu la sharika lah, lahu al-mulku wa lahu al-hamd, wa huwa 'ala kulli shay'in qadir' (There is no god but Allah, alone, without partner; to Him belongs the dominion and to Him belongs praise, and He has full power over all things). Then he would make a long supplication, sometimes raising his voice and sometimes lowering it, to the extent that among what he asked, he would ask Him to settle his debt. Then he would say the takbir three times, then say: 'La ilaha illallah' (There is no god but Allah) to the end. Then he would supplicate at length in the same way, until he had repeated this seven times. He did this on Safa and Marwah in every Hajj and Umrah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9347