It is reported that when a person stands at the grave of Rasulullah Sal’am and recites the verse:
Innallaha wa Malaa-Ikatahoo you Salloona Alan Nabee, and then says seventy times: Sallallahu Alayka ya Muhammad, an angel says: ‘May Allah’s blessings be on you too, and then Allah fulfills his every need.’
Hazrat Mullah Ali Qaari Rah is of the opinion that if in place of ‘Ya Muhammad’, once says ‘ya Rasulullah’ it would be better. Qastalani reported a similar opinion from Hazrat Shaikh Zainud-deen Maraghi Rah and others. The reason for this is that we have been prohibited from calling on the Holy Nabi by his name. (see Sharhi Mawaahib by Mullah Ali Qaari). However if in the Hadith quoted it says ya Muhammad, this should be taken into consideration and it then does not remain prohibited. I personally feel that a visitor to the grave should at every visit recite seventy times will complete humility: ‘Assalaatu Wassalaanu Alaika ya Rasulullah. This is best and better than to continue reciting in parrot fashion without understanding anything as s the custom.
Zurqaani says that seventy times have been chosen because the number is more likely to lead to acceptance. In the Qur’an Allah also mentioned the hypocrites in addressing the Nabi Sal’am: ‘Even though you should beg for forgiveness for them seventy times Allah will not forgive them.’