All perfect praise be to Allah The Lord of the Worlds and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Vaginal discharge (which scholars call "Rutubat Al-Farj") is a white discharge that many women have with or without a cause.Whether this discharge is pure or impure and whether it nullifies Wudu` or not, there are the following details:
1- If it comes out of the external part of the vagina, then it is pure (Tahir) and doesn`t nullify Wudu`.
2- If it comes out of the internal part of the vagina, then it is also pure, but nullifies Wudu`. Therefore, it is imperative that she makes Wudu` whenever she has this discharge. However, she doesn`t have to wash it off her clothes unless she is certain that it came from the depth of her womb similar to the discharge that comes upon delivery. In this case, it is impure (Najis) and requires washing the clothes off.
3- If she isn`t certain where the discharge came from, then it is pure and doesn`t nullify Wudu`, because certainty can`t be removed by doubt.
It is worth pointing out that the external part of the vagina is that which appears when a woman takes the position for answering the call of nature, and the internal part is what lies behind that. This is the conclusion arrived at by our jurists, as reported in the book {Boghyat Al-Mostarshideen, PP.53}. And Allah Knows Best.