Ibn Abi al-Zinad (may Allah have mercy on him) narrates from his father (may Allah have mercy on him), who narrates from the jurists of Madinah, that if a man said to his wife: "If you go out of the house before night, you are divorced," and his wife went out of the house; or he said that about his slave, and the slave left before night without informing him, then the woman is divorced and the slave is freed, because he omitted to make an exception. He was negligent in making the exception, so his negligence is held against him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15093