Sahih al-Bukhari — Fighting for the Cause of Allah (Jihaad) — Hadith No: 3064
Translation
Narrated Anas: The people of the tribes of Ril, Dhakwan, 'Usaiya and Bani Lihyan came to the Prophet (ﷺ) and claimed that they had embraced Islam, and they requested him to support them with some men to fight their own people. The Prophet (ﷺ) supported them with seventy men from the Ansar whom we used to call Al-Qurra'(i.e. Scholars) who (out of piety) used to cut wood during the day and pray all the night. So, those people took the (seventy) men till they reached a place called Bi'r-Ma'una where they betrayed and martyred them. So, the Prophet (ﷺ) invoked evil on the tribe of Ril, Dhakwan and Bani Lihyan for one month in the prayer. Narrated Qatada: Anas told us that they (i.e. Muslims) used to recite a Quranic Verse concerning those martyrs which was:-- "O Allah! Let our people be informed on our behalf that we have met our Lord Who has got pleased with us and made us pleased." Then the Verse was cancelled