Musnad Ahmad 1246:1

Abu Nu'aym narrated to us, he said: Al-Walid ibn Abdullah ibn Jumay' narrated to us, he said: Abd al-Rahman ibn Khallad al-Ansari and my grandmother narrated to me, from Umm Waraqah bint Abdullah ibn al-Harith, that the Prophet of Allah, peace and blessings of Allah be upon him, used to visit her every Friday. She said: "O Prophet of Allah—on the day of Badr—will you permit me to go out with you to nurse your sick and treat your wounded, so that perhaps Allah may grant me martyrdom?" He said: "Stay in your house, for Allah, the Mighty and Majestic, will grant you martyrdom." She had emancipated a slave girl and a slave boy of hers to be free after her death. It became long for them, so they smothered her with a velvet blanket until she died, and they fled. Umar was approached and it was said to him: "Umm Waraqah has been killed by her slave boy and her slave girl, and they have fled." Umar stood among the people and said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to visit Umm Waraqah and say: 'Let us go to visit the martyr.' And indeed, so-and-so, her slave girl, and so-and-so, her slave boy, have smothered her and then fled. Let no one harbor them, and whoever finds them, let him bring them." They were brought, and they were crucified, and they were the first to be crucified.