Midrash su Salmi 35:9

Rabbi Judan opened <his discourse> in the name of R. Ayyevu (with Ps. 32:9): DO NOT BE LIKE A HORSE OR A MULE, WITHOUT UNDERSTANDING….³²Tanh., Deut. 6:6; PRK 3:3; cf. PR 12:3. Six things are stated about the horse:³³Pes. 113b. (1) It eats much and (2) excretes little. (3) It loves promiscuity, (4) loves battle, (5) has a haughty spirit, (6) and abhors sleep. Moreover, there are also some who say: The horse wants to kill its master in battle. (Ibid.:) DO NOT BE LIKE A HORSE OR A MULE <WITH A BRIDLE AND A BIT>. ITS TRAPPINGS ARE FOR HOLDING IT IN CHECK. In the case of such a horse, when one bridles it, it balks. When one feeds it barley, it balks. When one pacifies it, it balks. When one approaches it, it balks {i.e., kicks}. You are not to be like that. Rather be careful [to repay] the good person for his goodness and to repay the evil person for his evil. (Deut. 25:17:) REMEMBER WHAT AMALEK DID TO YOU.