Musannaf Ibn Abi Shayba 6:1009

Muhammad ibn Abd Allah al-Asadi narrated to us, from Sufyan, from Alqama ibn Marthad, from Sulayman ibn Burayda, from his father, who said: When the Messenger of Allah (may Allah bless him and grant him peace) conquered Mecca, he came to a grave enclosure and sat by it. He acted as if he were speaking to someone, and the people sat around him. He then stood up while weeping. Umar met him—and he was among the boldest of people toward him—and said: "May my father and mother be sacrificed for you, O Messenger of Allah! What is it that has made you weep?" He said: "This is the grave of my mother. I asked my Lord for permission to visit it, and He granted me permission. I asked Him for permission to seek forgiveness for her, but He did not grant me permission. So I remembered her, and my soul felt sorrow, and I wept." He said: And a day was never seen in which there was more weeping than on that day.