Sunan Abi Dawud Book 2, Hadith 202
The Messenger of Allah(ﷺ) used to visit her at her house. He appointed a mu’adhdhin to call adhan for her; and he commanded her to lead the inmates of her house in prayer. ‘Abd al-Rahman said: I saw her mu’adhdhin who was an old man.
When the Prophet (ﷺ) proceeded for the Battle of Badr, I said to him: Messenger of Allah allow me to accompany you in the battle. I shall act as a nurse for patients. It is possible that Allah might bestow martyrdom upon me. He said: Stay at your home. Allah, the Almighty , will bestow martyrdom upon you.
The narrator said: Hence she was called martyr. She read the Qur'an. She sought permission from the Prophet (ﷺ) to have a mu'adhdhin in her house. He, therefore, permitted her (to do so).
She announced that her slave and slave-girl would be free after her death. One night they went to her and strangled her with a sheet of cloth until she died, and they ran away.
Next day Umar announced among the people, "Anyone who has knowledge about them, or has seen them, should bring them (to him)."
Umar (after their arrest) ordered (to crucify them) and they were crucified. This was the first crucifixion at Medina.
The Prophet (ﷺ) said: There are three types of people whose prayer is not accepted by Allah: One who goes in front of people when they do not like him; a man who comes dibaran, which means that he comes to it too late; and a man who takes into slavery an emancipated male or female slave.