What is the ruling on dealing with a colleague who is ill-mannered, makes false accusations, and invokes evil, knowing that he is religious, fasts, and prays at night?

If you know that you have treated the person mentioned with fairness and justice and have not wronged them, then do not fear their supplication. You both must cease the reviling and mutual cursing, for insulting a Muslim is a transgression. You should be patient, suppress your anger, and forgive the one who wrongs you, seeking Allah's pleasure, for He Almighty says: "and those who suppress anger and pardon people." "And Allah does not increase a servant by forgiveness except in honor." However, if you are the one who committed injustice, then you must repent to Allah and seek forgiveness from them in this world, before it is taken from you in the Hereafter. "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness before it is taken from him at a time when there will be no dinar or dirham."