What is the ruling on a husband telling his wife, "If your mother stays overnight in the house, you are of no use to me," then her mother stays overnight in the house without him being informed? Is this considered a divorce?

All praise is due to Allah. A divorce made conditional upon an event occurs when that event takes place. Divorce can occur explicitly, such as by saying, "You are divorced," without the need for intention, or implicitly, such as by saying, "Go to your family," provided there is an intention. If it is the first or second divorce, he may take her back during her waiting period (iddah). If it is the third divorce, she is not lawful for him until she marries another husband. You should consult the Sharia courts.