Sahih al-Bukhari 234
Sahih al-Bukhari · Book 4: Ablutions (Wudu') · (What is said) about the urine of camels, sheep and other animals and about their folds
Narrated Anas:
حَدَّثَنَا آدَمُ ، قَالَ حَدَّثَنَا شُعْبَةُ ، قَالَ أَخْبَرَنَا أَبُو التَّيَّاحِ، يَزِيدُ بْنُ حُمَيْدٍ عَنْ أَنَسٍ ، قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم يُصَلِّي قَبْلَ أَنْ يُبْنَى الْمَسْجِدُ فِي مَرَابِضِ الْغَنَمِ.
Prior to the construction of the mosque, the Prophet (ﷺ) offered the prayers at sheep-folds.