Musannaf Ibn Abi Shayba 21:526

Muhammad ibn al-Fudayl narrated to us, from al-Ala’ ibn al-Musayyab, from his father, who said: When Umar would pass through the valley between al-Safa and al-Marwah, he would hasten in it, saying: "My Lord, forgive and have mercy, for You are the Most Mighty, the Most Generous."