Abu Musa's Uncle, and the Rule on Non-Combatants

Shaykh Yasir Qadhi explains:

In the pursuit of Hawāzin, the uncle of Abū Mūsā al-Ashʿarī, a commander, was run through with a javelin. Abū Mūsā slew the man who did it before his uncle's eyes, then drew out the javelin; his uncle, bleeding to death, sent his salām to the Prophet ﷺ and begged his duʿāʾ. The Prophet ﷺ rose from his shawl, called for water, made wuḍūʾ, faced the qiblah and raised his hands until his armpits showed, praying, "O Allāh, raise his rank and forgive his sins", and, when Abū Mūsā asked, for him too. (Abū Mūsā's son Abū Burda became a great scholar of the Tābiʿūn, proud that the Prophet ﷺ had prayed for his father and grandfather both.)

Walking the field afterward, the Prophet ﷺ saw a slain woman and was angered: "She should not have been killed." He sent word to the commander ahead that he was to kill no woman, child, or servant, the basis of the famous ruling, central in every book of fiqh, that non-combatants may not be killed in war.