Hadith 8:3017
Abu Bakr narrated to us, he said: Jarir narrated to us, from Mansur, from Ibrahim, from Layth and Mujahid, they both said: "The *sawwaf* (horses standing on four legs) are upon four, and the *sawafin* (horses standing on three legs, with the tip of the fourth hoof touching the ground) are upon three."
حدثنا أبو بكر قال نا جرير عن منصور عن إبراهيم عن ليث ومجاهد قالا الصواف على أربعة والصوافن على ثلاثة