Q: Is Nikah (marriage) valid if contracted in the state of major ritual impurity?
A: Nikah in an impure state is valid. Once a person said QABILTU-HAA the nikah is valid whether that person was paak or naapaak. But remember that if the nikah is performed in a musjid, then the person who entered the musjid in this naapaak state has committed a major sin. Even though the nikah is valid, but it is a big sin to enter a musjid in an impure state.
Mufti Siraj Desai