Musnad Abu Ya'la al-Mawsili 95:6

Abu Ali Ahmad ibn Ibrahim al-Mawsili narrated to us, Abu Fadala Faraj ibn Fadala narrated to us, from Abd al-Khabir ibn Qays ibn Thabit ibn Shammas, from his father, from his grandfather, who said: A man from the Ansar named Khallad was killed on the day of Qurayza. It was said to his mother, "O mother of Khallad, Khallad has been killed." She came while she was veiled. It was said to her, "Khallad has been killed, and you come to us veiled?" She said, "If I have been afflicted with the loss of Khallad, I shall not be afflicted with the loss of my modesty." They mentioned that to the Prophet, peace and blessings of Allah be upon him, and he said, "As for him, he has the reward of two martyrs." It was said, "O Messenger of Allah, and why is that?" He said, "Because the People of the Book killed him."