Ata' (may Allah have mercy on him) narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that in the days of ignorance (Jahiliyyah), ila used to be for one or two years or even more, but Allah, Lord of Might, fixed its time at four months, if someone wishes to take an oath of ila. In the narration of Yunus: Whoever takes an oath of ila for less than four months, that will not be ila.
Ata' (may Allah have mercy on him) said: If the husband takes an oath of ila while the wife is still in her parents' house and has not yet been sent to him, that will not be ila.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإيلاء / 15237