Ibn Tawus (may Allah have mercy on him) narrates from his father (may Allah have mercy on him) concerning ila (al-ila') that the husband swears not to have intercourse forever, or for six months or more, or for more than four months, or something similar.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإيلاء / 15238