It is narrated from Yahya bin Bishr, Ikrimah (may Allah have mercy on him) said: (Its duration) is one month. Imam Darimi (may Allah have mercy on him) was asked: What is your opinion? He replied: Three months is a precautionary strong duration, and one month is also sufficient.
Hadith Referenceسنن دارمي / من كتاب الطهارة / 1215