Sunan an-Nasa'i, Volume 2, Book 11, Hadith 974 (DarusSalam) ⓘ

It was narrated that Abu Sa'eed Al-Khudri said: "The Iqamah for Zuhr prayer would be said, and a person could go to the Al-Baqi', relieve himself, perform wudhu, and come (to the masjid), and the Messenger of Allah would still be in the first rak'ah, making it lengthy.

أَخْبَرَنَا عَمْرُو بْنُ عُثْمَانَ، قَالَ حَدَّثَنَا الْوَلِيدُ، عَنْ سَعِيدِ بْنِ عَبْدِ الْعَزِيزِ، عَنْ عَطِيَّةَ بْنِ قَيْسٍ، عَنْ قَزَعَةَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ لَقَدْ كَانَتْ صَلاَةُ الظُّهْرِ تُقَامُ فَيَذْهَبُ الذَّاهِبُ إِلَى الْبَقِيعِ فَيَقْضِي حَاجَتَهُ ثُمَّ يَتَوَضَّأُ ثُمَّ يَجِئُ وَرَسُولُ اللَّهِ صلى الله عليه وسلم فِي الرَّكْعَةِ الأُولَى يُطَوِّلُهَا ‏.‏