Is it permissible to supplicate: "O Lord, whatever reward You have not prescribed for me – for any good deed – then prescribe the like of it for all Muslims, those living and those dead, and those who are to come"?

It is preferable for a Muslim to supplicate with comprehensive prayers that encompass the good of this world and the the Hereafter, especially those that are authentically reported. The best supplication for Muslims is to seek forgiveness for them, as the prophets did and as Allah commanded His Prophet Muhammad, peace and blessings be upon him. It is permissible to supplicate with the form "O Allah, convey the reward of what we have recited to so-and-so," and supplicating for all Muslims includes those who have not yet come.