Avraham Avinu mother was a Nida when she conceived him:
In the writings of the Arizal it states as follows: There are many very holy and high souls that are born to ignoramuses and evil men, such as Avraham from his father Terach. It states in the Zohar that Terach was intimate with his wife when she was a Nida and from that union was born Avraham. The reason that God arranged this is because he had fool the side of evil to allow this very high soul to come down, as the side of evil was unaware that this would be the precise way in how this divine soul would then be fixed. It is due to this reason that Terach was later reincarnated into Iyov, and was stricken with boils, as one who has relations with a Nida get stricken with leprosy. It is also due to this reason that Avraham was thrown into the fire in order to cleanse him from this impurity that he was born from.
 Shaar Hagilgulim p. 62, Hakdama 38