What is the ruling on the suitor telling his fiancée: "You will be unlawful to me when we marry if you speak about anything outside of work"?

The engaged man and woman are considered strangers to each other before the marriage contract, and privacy (khalwa) between them is not permissible.

If the fiancé makes something forbidden (tahreem) contingent upon his fiancée speaking about a topic unrelated to work, then he will break his oath if she speaks about that topic.

His intention behind the tahreem is considered: - If he intended a promise of divorce, then nothing is binding upon him if he does not fulfill his promise. - If he intended to execute a divorce after the marriage contract, it does not take effect according to many scholars, and this is the most preponderant opinion. - If he intended ẓihār (a statement equating one's wife to a forbidden relative), then it becomes binding upon him, and he must pay an expiation after marriage and before intercourse. - If he intended an oath by Allah Almighty, or if he had no specific intention, then an expiation for breaking an oath becomes binding upon him.

A woman's work in a mixed-gender environment is not permissible except out of necessity, provided that privacy (khalwa) and handshakes are avoided, speech is limited to what is necessary without softening the voice, and full hijab is worn.