A person must be very careful to avoid anger altogether, at all times. Our Rabbis of Blessed Memory told us, "Whoever gets angry, if he is a wise person, his wisdom leaves him...".
Rabbenu the Ari zal, was stricter about anger than any other transgression, even if the anger was over a Miswah (commandment) as happened with Moshe Rabbenu, 'a"h, who got angry for G-d's sake and, nevertheless, forgot Halakha as a result.
He states that one who gets angry has no rectification for his sin till he tries with all his might and overcomes this trait and does not get angry at all.
(See Pesahim 66b. Wayiqra 10:17. Kaf Hahayim 170, Oth 30)
