Musannaf Ibn Abi Shayba 18:1171

Abu Bakr narrated to us, he said: Muhammad ibn Fudayl narrated to us, from Layth, from ‘Amr ibn Shu’ayb, who said: ‘Umar wrote to me regarding a woman who grabbed a man’s testicles and tore the skin, but did not tear the membrane (al-sifaq). ‘Umar said to his companions, “What do you see regarding this?” They said, “Treat it as the status of a *ja’ifah* (a wound that reaches the body cavity).” ‘Umar said, “But I see otherwise. I see that in it is half of what is in the *ja’ifah*.”