Musannaf Ibn Abi Shayba 34:118

Al-Fadl narrated to us, Al-Walid ibn Jumay' narrated to us, he said: My grandmother narrated to me, from Umm Waraqah bint 'Abd Allah ibn al-Harith al-Ansari, that a male slave of hers and a female slave of hers smothered her and killed her during the caliphate of 'Umar. And they fled, so 'Umar had them brought, and he crucified them. They were the first to be crucified in al-Madinah.