Sunan Ibn Majah, Hadith 616 ⓘ
It was narrated that 'Abdullah bin Arqam said: "The Messenger of Allah said: 'If anyone of you needs to defecate and the immediate call to prayer (Iqamah) is given, let him start with (relieving himself).'"
حَدَّثَنَا مُحَمَّدُ بْنُ الصَّبَّاحِ، أَنْبَأَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَبْدِ اللَّهِ بْنِ أَرْقَمَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " إِذَا أَرَادَ أَحَدُكُمُ الْغَائِطَ وَأُقِيمَتِ الصَّلاَةُ فَلْيَبْدَأْ بِهِ " .
also referenced under: Book 1, Hadith 659 (In-Book) & Volume 1, Book 1, Hadith 616 (DarusSalam)