Nafi' (may Allah have mercy on him) said that whenever Ibn Umar (may Allah be pleased with them both) returned from a journey, he would enter the mosque, then come to the grave of the Prophet (peace and blessings be upon him) and say: 'As-salamu alayka ya Rasulallah' (Peace be upon you, O Messenger of Allah), 'As-salamu alayka ya Aba Bakr' (Peace be upon you too, O Abu Bakr), 'As-salamu alayka ya abati' (Peace be upon you too, O my father).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10271