﴿ مَّا كَانَ مُحَمَّدٌ أَبَآ أَحَدٍۢ مِّن رِّجَالِكُمْ وَلَٰكِن رَّسُولَ ٱللَّهِ وَخَاتَمَ ٱلنَّبِيِّۦنَ ۗ وَكَانَ ٱللَّهُ بِكُلِّ شَىْءٍ عَلِيمًۭا ﴾

“[And know, O believers, that] Muhammad is not the father of any one of your men, but is God’s Apostle and the Seal of all Prophets. And God has indeed full knowledge of everything.”

Muhammad is not the father of any man among you he is not Zayd’s biological father and so it is not unlawful for him to marry his former wife Zaynab after him; but he is the Messenger of God and the Seal of the Prophets and so he will not have a son that is a fully grown man to be a prophet after him a variant reading for khātim al-nabiyyīna has khātam al-nabiyyīn as in the instrument known as a ‘seal’ in other words their prophethood has been sealed by him. And God has knowledge of all things among these is the fact that there will be no prophet after him and even when the lord Jesus descends at the end of days he will rule according to his Muhammad’s Law.