Sunan Abi Dawud 2488

Narrated Thabit ibn Qays: A woman called Umm Khallad came to the Prophet (ﷺ) while she was veiled. She was searching for her son who had been killed (in the battle) Some of the Companions of the Prophet (ﷺ) said to her: You have come here asking for your son while veiling your face? She said: If I am afflicted with the loss of my son, I shall not suffer the loss of my modesty. The Messenger of Allah (ﷺ) said: You will get the reward of two martyrs for your son. She asked: Why is that so, Messenger of Allah? He replied: Because the people of the Book have killed him