Musar zu Bamidbar 20:10

Anger leads to mistakes. Who is a greater man than Moses, our teacher? Moses, upon him be peace, was angry in three places, and he made what would generally be termed "mistakes". As it is said : "And he was angry with Eleazar and with Ithamar" (Lev. 10:16), and it is written : "Why did you not eat the sin-offering in the sacred area?" (Lev. 10:17). And it is said : "Listen, you rebels" (Num. 20:10) and it is said : "And he struck the rock" (Ib. : 11). And it is said : "Moses became angry with the commanders of the army" (Num. 31:14), and it is written : "And Eleazar the priest said to the troops who had taken part in the fighting This is the ritual law' " (Num. 31:21). Which teaches that Moses forgot the law (while angry) (Leviticus Rabbah 13:1). And so, you can understand that if these things happened to Moses peace be upon him, when he was angry, what can happen to fools who are angry! And therefore Solomon said, "Be not hasty in thy spirit to be angry" (Eccl. 7:9).