Musannaf Ibn Abi Shayba 18:449

Abu Bakr narrated to us, he said: Ma'n ibn 'Isa narrated to us, from Ibn Abi Dhi'b, from al-Zuhri, who said: He was asked about a woman's breast, and he said: "In it is half of the blood money (diyah)." And if a part of it is injured, then in it is a fair assessment (hukumat 'adl) by the jurist (mujtahid).