Yahya related to me from Malik that Abdullah ibn Dinar said, "Isaw Abdullah ibn Umar stop by the grave of the Prophet, may Allahbless him and grant him peace, and ask for blessings on the Prophet,may Allah bless him and grant him peace, and on Abu Bakr and Umar."
USC-MSA web (English) reference: Book 9, Hadith 71
Arabic reference: Book 9, Hadith 402