If the husband is impotent or dies childless, the wife can conceive from a brother-in-law. This is called niyoga and is allowed only in the case of childlessness. A woman can do niyoga only for one child or a maximum of two. After the successful union, if the brother-in-law is younger, he treats the woman as his mother. If he is elder, he treats her as his daughter-in-law. Niyoga should be at night. The man has to wear white clothes and apply ghee all over his body for purity. The man and woman have to keep their mind pure and be clear that the act is only for begetting a child. If a prospective bridegroom dies after the engagement, the woman can go for niyoga. (Manu Smriti.9)