Reference for Avodah Zarah 50:2

לא צריכא באשתו עמו עובד כוכבים אין אשתו משמרתו אבל ישראל אשתו משמרתו

It is necessary in a case where the man's wife is present. An idolater, his wife will not prevent him, but the wife of an Israelite will prevent him.

Jastrow