Narrated Thabit ibn Qays (Radhiallaahu Ánhu): A woman called Umm Khallad came to the Prophet (Sallallaahu Álayhi Wasallam) while she was veiled. She was searching for her son who had been killed (in the battle) Some of the Companions of the Prophet (Sallallaahu Álayhi Wasallam) 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
. Rasulullah (Sallallaahu Álayhi Wasallam) said: You will get the reward of two martyrs for your son. She asked: Why is that so, oh Prophet of Allah? He (Sallallaahu Álayhi Wasallam) replied: Because the people of the Book have killed him.
(Abu Dawood Book 14, Hadith # 2482)