Is it permissible to visit the deceased before the forty-day period, and is there any evidence for this from the sayings of the Prophet, peace and blessings be upon him, or any other reference?

There is no harm for a Muslim in visiting graves at any time. It is a recommended act for remembering death and the Afterlife and for taking admonition. The Prophet, peace be upon him, commanded it after he had initially forbidden it. There is nothing that prevents visiting them before forty days from burial; this has no basis. Scholars have differed regarding women visiting graves. The majority permitted it, interpreting the prohibition as applying to frequent visitation, not to the act of visiting itself. They based their argument on the Prophet's, peace be upon him, approval of the woman who was weeping at a grave and his teaching 'Aisha the supplication for visiting graves, provided that it is free from forbidden acts. It should be noted that holding mourning ceremonies and celebrating the fortieth day remembrance for the deceased is an innovation not found in Islamic law.