Sayyiduna Abdullah bin Umar, may Allah be pleased with them both, used to say: Whoever makes an oath of abstinence (ila) from his wife, when four months have passed, the husband should be compelled before the ruler to either divorce or return; he should revoke the ila and have intercourse. And if four months pass without divorce, divorce will not take effect upon the woman.
Hadith Referenceموطا امام مالك رواية يحييٰ / كتاب الطلاق / 1150