Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) visited the grave of his mother, and he (peace and blessings be upon him) wept and made those around him weep. He (peace and blessings be upon him) said: "I asked my Lord for permission to seek forgiveness for her, but I was not given permission. Then I asked for permission to visit her grave, and it was given to me. So visit the graves, for they certainly remind you of death."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7192