Musnad Ahmad 27:1124

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from 'Amr ibn Dinar, I heard 'Abdullah ibn 'Umar saying: When the Messenger of Allah (peace and blessings of Allah be upon him) arrived in Makkah, he performed Tawaf around the House seven times, then he prayed two rak'ahs at the Maqam (Station of Ibrahim), then he went out to Al-Safa from the gate through which he goes out, and he performed Sa'i between Al-Safa and Al-Marwah. He said: And Ayyub informed me, from 'Amr ibn Dinar, from Ibn 'Umar, that he said: It is a Sunnah.