Musnad Ahmad 790:112

Abu ‘Amir narrated to us, Hisham narrated to us, from Yahya, from Abu Qilabah, from Abu al-Muhallab, from ‘Imran ibn Husayn, that a woman from Juhaynah came to the Prophet, peace and blessings of Allah be upon him, while she was pregnant from adultery. She said: "O Messenger of Allah, I have committed a transgression that warrants a prescribed punishment, so execute it upon me." The Messenger of Allah, peace and blessings of Allah be upon him, called her guardian and said: "Treat her well, and when she delivers her child, bring her to me." He did so, and he (the Prophet) ordered that her clothes be tied securely upon her, then he ordered that she be stoned. Then he prayed over her. ‘Umar said to him: "Do you pray over her when you have stoned her?" He replied: "She has repented with a repentance that, if it were divided among seventy of the people of Medina, it would suffice them. And have you found anything better than that she offered her soul to Allah?"