Language:
كتاب الغسل
5
Bathing (Ghusl)
(17)
Chapter: If someone while in the mosque remembers that he is Junub, he should leave (the mosque to take a bath) and should not perform Tayammum
(17)
باب إِذَا ذَكَرَ فِي الْمَسْجِدِ أَنَّهُ جُنُبٌ يَخْرُجُ كَمَا هُوَ وَلاَ يَتَيَمَّمُ

Narrated Abu Huraira:

Once the call (Iqama) for the prayer was announced and the rows were straightened. Allah's Messenger (ﷺ) came out; and when he stood up at his Musalla, he remembered that he was Junub. Then he ordered us to stay at our places and went to take a bath and then returned with water dropping from his head. He said, "Allahu-Akbar", and we all offered the prayer with him.

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ، قَالَ حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ، قَالَ أَخْبَرَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ أُقِيمَتِ الصَّلاَةُ، وَعُدِّلَتِ الصُّفُوفُ قِيَامًا، فَخَرَجَ إِلَيْنَا رَسُولُ اللَّهِ صلى الله عليه وسلم فَلَمَّا قَامَ فِي مُصَلاَّهُ ذَكَرَ أَنَّهُ جُنُبٌ فَقَالَ لَنَا ‏:‏ ‏ "‏ مَكَانَكُمْ ‏"‏‏.‏ ثُمَّ رَجَعَ فَاغْتَسَلَ، ثُمَّ خَرَجَ إِلَيْنَا وَرَأْسُهُ يَقْطُرُ، فَكَبَّرَ فَصَلَّيْنَا مَعَهُ‏.‏ تَابَعَهُ عَبْدُ الأَعْلَى عَنْ مَعْمَرٍ عَنِ الزُّهْرِيِّ‏.‏ وَرَوَاهُ الأَوْزَاعِيُّ عَنِ الزُّهْرِيِّ‏.‏
Reference : Sahih al-Bukhari 275
In-book reference : Book 5, Hadith 27
USC-MSA web (English) reference : Vol. 1, Book 5, Hadith 274
  (deprecated numbering scheme)