Musannaf Ibn Abi Shaybah 12168 — Those who permitted visiting graves

It is narrated from Sayyiduna Abdullah (bin Mas'ud) (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Indeed, I had (earlier) forbidden you from visiting the graves. Indeed, I have been given permission to visit the grave of my mother. So you too should visit the graves; it will remind you of the Hereafter."