What is the ruling on uttering the word "woe" unintentionally, and does it nullify good deeds and require expiation?

"Woe" (الويل) is a word of warning and threat, signifying disgrace, torment, and destruction. It encompasses every punishment, sorrow, torment, and fear. It is permissible to use it with the intention of warning and threatening against an act that violates the Sharia, such as the Prophet's (peace be upon him) saying: "Woe to the heels from the Fire." However, it is not permissible to use it for a matter of permissible scholarly disagreement, or for violating a non-obligatory Sunnah. It is also not permissible to invoke it against oneself unless it is in a conditional form, like the saying of Umar (may Allah be pleased with him): "Woe to me and woe to my mother if He does not forgive me." As for the claim that it nullifies good deeds, that is incorrect and without proof. Whoever uses it in an inappropriate context should seek Allah's forgiveness and not repeat it.