Miqsam said: I heard Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) saying: The resolve to divorce is after four months have passed, while fay' (returning) means intercourse.
This is the authentic report from Abdullah bin Abbas (may Allah be pleased with them both), though the opposite has also been narrated from him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإيلاء / 15230