Ali ibn al-Husayn (may Allah be pleased with him) informs us that he saw a man invoking Allah at the grave of the Prophet (may Allah's peace and blessings be upon him). He forbade the man from doing so based on a Hadīth in which the Prophet (may Allah's peace and blessings be upon him) forbade visiting his grave repeatedly, and also forbade non-observance of remembering Allah and worshiping Allah at homes, thereby rendering them similar to graves. The Prophet (may Allah's peace and blessings be upon him) said that sending peace upon him will definitely reach him, regardless of the sender's whereabouts.