Musannaf Ibn Abi Shayba 11:22

Waki’ narrated to us, he said: Al-Mas’udi narrated to us, from ‘Amr ibn Murrah, from ‘Abdullah ibn al-Harith, from ‘Abdullah ibn ‘Amr, he said: A man said: "O Messenger of Allah, which Jihad is the most excellent?" He said: "He whose horse is hamstrung and his blood is spilled."