وَيَقْتَدِي بِهِ الْمَهْدِيُّ لِأَنَّهُ أَفْضَلُ
And the Mahdi will follow him in prayer, because he is more excellent.
The surrounding discussion cites reports about Jesus' return and leadership in prayer. Narrations differ in some details of the specific event and who leads whom. Those subsidiary particulars must be distinguished from the central claim: the return does not abrogate Muhammad's finality or his religious law.
Abrogation refers to a previously established rule being superseded by subsequent revelation. An earlier prophet returning and acting according to the final law is not itself an instance of abrogation.