Is it permissible for a Muslim to say: "Imam Malik is not a Messenger; he is right sometimes and wrong sometimes in his fatwas?"

It is correct to use this phrase when referring to the mujtahid imams, such as Imam Malik, provided that it is not accompanied by any disparagement or belittlement. One must be cautious about slandering scholars, for their flesh is poisonous, and they are the inheritors of the prophets. Honoring them is a part of honoring Allah Almighty.