Muwatta 1607

Malik says that whoever swears not to have intercourse with his wife for a day or a month, and then waits until more than four months have passed, is not making ila. Ila, with stopping, applies only to one who swears for more than four months. As for one who swears for four months or less, Malik sees no ila on him, since when the term at which he would be stopped arrives he is out of his oath, and no stopping applies. ¹

Belongs to the Muwatta, Book of Divorce. Source: the Muwatta. Mentions Malik ibn Anas. Built on in the chapters on ila.