There were seventy young men from the Ansar known as the Qurra, the reciters. They would stay in the mosque, and when evening came they would withdraw to a corner of Madinah where they would study and pray together. Their families thought they were in the mosque, while the people of the mosque thought they were with their families. As dawn approached, they would fetch fresh water and gather firewood, bringing it back and leaving it beside the chamber of the Messenger of Allah ﷺ.The Prophet ﷺ sent them all out on an expedition, and they were killed on the day of Bir Mauna. The Prophet ﷺ then invoked Allah against their killers for fifteen days during the dawn prayer.
حدثنا عبيدة بن حميد عن حميد الطويل
كان شباب من الأنصار سبعين رجلا يقال لهم القراء قال كانوا يكونون في المسجد فإذا أمسوا انتحوا ناحية من المدينة فيتدارسون ويصلون يحسب أهلوهم أنهم في المسجد ويحسب أهل المسجد أنهم في أهليهم حتى إذا كانوا في وجه الصبح استعذبوا من الماء واحتطبوا من الحطب فجاءوا به فأسندوه إلى حجرة رسول الله ﷺ فبعثهم النبي ﷺ جميعا فأصيبوا يوم بئر معونة فدعا النبي ﷺ على قتلتهم خمسة عشر يوما في صلاة الغداة
No references are available.
Its isnad is sahih. Ubayda bin Humayd Kufi Haddaa was deemed reliable by the scholars, and his hadith is found in Bukhari. The hadith was mentioned earlier at 12342.