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
There are two reported opinions regarding the waiting period (‘iddah) of a slave woman (bondwoman) for istibra’ (to ascertain if she is pregnant). Some scholars have said that her waiting period is three months, like that of a free woman. Some scholars have said that, due to her being a slave woman, her period of istibra’ is half that of a free woman, i.e., 45 days.
Imam Darimi rahimahullah has stated: Three months is better, and one month is sufficient. This is so that it may be ascertained whether she is pregnant or not, for in such a case, intercourse with her would not be permissible.
Furthermore, within this period, the womb of the slave woman will be cleansed, and, by Allah’s permission, there will no longer be a risk of another man’s sperm remaining.