What is the ruling on the false testimony given by the questioner to protect her mother-in-law from her ex-husband, who is threatening her and her children? What is its expiation? And how can she get rid of his threats?

Perjury is one of the gravest sins, and the intention of reaching the truth does not make it permissible. Rather, the truth must be reached through lawful means. Whoever has committed perjury must offer sincere repentance by abandoning the sin, feeling remorse, and resolving never to return to it. If his testimony caused harm to another, he must retract his testimony and seek forgiveness from the one against whom he testified. If no harm resulted, then repentance between him and Allah suffices. As for how to get rid of the evil of this man, that is a matter for the authorities and specialists.