The rain was falling on the day when the Battle of Hunayn took place. The Prophet ﷺ, therefore, commanded that the people should offer their prayer in their camps. (Using translation from Abū Dāʾūd 1057)
أَنَّ يَوْمَ حُنَيْنٍ كَانَ يَوْمًا مَطِيرًا فَأَمَرَ النَّبِيُّ ﷺ مُنَادِيَهُ أَنَّ الصَّلَاةَ فِي الرِّحَالِ