If somebody is leading the Salat (prayer) and (in the meanwhile) the first (usual) Imam comes, the Salat is valid whether the former retreats or does not retreat
حَدَّثَنَا قَبِيصَةُ، حَدَّثَنَا سُفْيَانُ، عَنْ زَيْدِ بْنِ أَسْلَمَ، قَالَ سَمِعْتُ ابْنَ عُمَرَ، يَقُولُ جَاءَ رَجُلاَنِ مِنَ الْمَشْرِقِ فَخَطَبَا فَقَالَ النَّبِيُّ صلى الله عليه وسلم إِنَّ مِنَ الْبَيَانِ لَسِحْرً"
Narrated Ibn `Umar:
Two men came from the east and delivered speeches, and the Prophet (ﷺ) said, "Some eloquent speech has the in fluency of magic (e.g., some people refuse to do something and then a good eloquent speaker addresses them and then they agree to do that very thing after his speech). "
Reference: Sahih al-Bukhari 5146 In-book : Book 67, Hadith 81 USC-MSA web (English) : Vol. 7, Book 62, Hadith 76 (deprecated)
Help us gift a modern, ad-free Islamic application for the Muslim Ummah. Your donation will be recorded as Sadaqah Jariyah in your book of deeds, In Sha Allah.