Musannaf Ibn Abi Shayba 18:917

Abu Bakr narrated to us, he said: Abu Khalid narrated to us, from Hajjaj, from [Abu] Awn, from Shurayh: That a youth jumped upon another, so the one underneath moved aside, and the front tooth of the one on top broke. So he held the one on top liable, and did not hold the one underneath liable.