The issue of PBUH
Question:

Are we obliged in the Quran to write the words “Peace be upon him” (PBUH) after the name of prophet Muhammad or any of God’s messenger whenever we mention their names?

Reply:

There is no obligation in the Quran to use these words after the name of any of God’s messengers and prophets. The Quran tells us that it is perfectly alright to say the names of any of the prophets without any additions: The prophets and messengers were men chosen by God to deliver His messages, but at the end of the day they were ordinary men who will stand in front of God to receive their judgement like all others.

Say, "We believe in God and in what was brought down to us, and in what was brought do
wn to Abraham, Ishmael, Isaac, Jacob and the Tribes, and in what was given to Moses and Jesus, and what was given to the prophets from their Lord. We make no distinction among any of them and to Him we are Submitters." 2:136

The word
"Say" in the beginning of the above verse is in the plural. It means that we should all say the words in 2:136, and we should say them as they are and without additions. We do not see the words PBUH after the name of any of the prophets mentioned in 2:136, do we?
Muhammad is one of the prophets of God. He was not any different from the other messengers of God:

Say (O Muhammad), "I am not a novelty among the messengers, nor do I know what will happen to me or to you. I follow nothing other than what is revealed to me. I am no more than a clear warner. 46:9

Thus, what applies to the prophets of God applies to Muhammad as well. If we should give Muhammad preferential treatment above the prophets mentioned in 2:136, we would have disobeyed God’s command in 2:285 for not making any distinction between any of His messengers.