Ibn Al-Hisham in Saheeh Al-Sirah, Pg117 says:
(Aboo Bakr) saw that Umar Ibn Al-Khattab was torturing a slave-girl of Bani Mo’ammal from the family
of Adee Ibn Ka’b to force her to leave the religion of Islam, and Umar at that time was a polytheist
(Mushrik). He hit her until he was tired, then he said: "I apologise to you that I had to stop hitting
you, that is only because I got tired" whereupon she said, "Allah (swt) will do the same to you!" And
then Aboo Bakr bought her and freed her.
Alkarbala