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 عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنْ إِسْرَائِيلَ، عَنْ أَبِي إِسْحَاقَ، عَنِ الأَسْوَدِ، قَالَ قَالَ لِي ابْنُ الزُّبَيْرِ كَانَتْ عَائِشَةُ تُسِرُّ إِلَيْكَ كَثِيرًا فَمَا حَدَّثَتْكَ فِي الْكَعْبَةِ قُلْتُ قَالَتْ لِي قَالَ النَّبِيُّ صلى الله عليه وسلم يَا عَائِشَةُ، لَوْلاَ قَوْمُكِ حَدِيثٌ عَهْدُهُمْ ـ قَالَ ابْنُ الزُّبَيْرِ بِكُفْرٍ ـ لَنَقَضْتُ الْكَعْبَةَ فَجَعَلْتُ لَهَا بَابَيْنِ باب يَدْخُلُ النَّاسُ، وَبَابٌ يَخْرُجُونَ " فَفَعَلَهُ ابْنُ الزُّبَيْرِ
Narrated Aswad:
Ibn Az-Zubair said to me, "Aisha used to tell you secretly a number of things. What did she tell you about the Ka`ba?" I replied, "She told me that once the Prophet (ﷺ) said, 'O `Aisha! Had not your people been still close to the pre-Islamic period of ignorance (infidelity)! I would have dismantled the Ka`ba and would have made two doors in it; one for entrance and the other for exit." Later on Ibn Az-Zubair did the same.
Reference: Sahih al-Bukhari 126 In-book : Book 3, Hadith 68 USC-MSA web (English) : Vol. 1, Book 3, Hadith 128 (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.