Is it permissible to invoke blessings upon the Prophet, peace be upon him, with the wording: "O Allah, bless Muhammad as many times as the pilgrims have performed Hajj..."? Is it permissible to include the Companions when invoking blessings upon him? And what prevents saying: "عليه السلام" (upon him be peace)?

The most cautious and complete way to send blessings upon the Prophet (peace and blessings be upon him) and to supplicate is to limit oneself to the wordings narrated from him. It is permissible to send blessings upon the Prophet (peace and blessings be upon him) using wordings not narrated from him. Scholars have differed regarding the permissibility of sending blessings upon the Companions. The most preponderant opinion is that it is generally permissible to send blessings upon prophets, angels, the Prophet's descendants, and people of obedience. However, it is disliked to specifically send blessings upon an individual if it is taken as a slogan. As for sending salutations upon others besides prophets, it is legislated as a greeting to a living person. Scholars have differed on the permissibility of singling out an individual with it.