(56) باب تَطْوِيلِ الْقِيَامِ فِي الرَّكْعَةِ الأُولَى مِنْ صَلاَةِ الظُّهْرِ
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 (ﷺ) would still be in the first rak'ah, making it lengthy.
Reference: Sunan an-Nasa'i 973
In-book reference: Book 11, Hadith 98
English translation: Vol. 2, Book 11, Hadith 974