What is the ruling of Sharia on a man's telling his wife: "You are a wicked woman (fajirah)," and a wife's telling her husband: "Allah is between me and you," in a moment of anger?

The Hanbalis and Shafi’is held that words capable of being interpreted as slander (qadhf) or otherwise should be referred to the intention of the speaker. If the speaker intended slander, then the prescribed punishment (hadd) is due; otherwise, it is not, but the person should be disciplined and reprimanded.

If a man says to his wife, "O immoral one" (ya fajirah) without cause, it is forbidden and an act of wickedness. However, if he says it due to a reason, such as insubordination (nushooz), and does not intend to accuse her of immorality, then there is nothing against him, for Allah Almighty says: ﴿Allah does not like the public utterance of evil speech, except by one who has been wronged﴾.

As for the wife’s statement to her husband, "Allah is between me and you," there is nothing against her for it, especially if it is in response to his injustice.