Can You Pray With Discharge on Your Underwear?
Question

A girl noticed some thin discharge on her underwear but she had not felt it come out. Is it permissible for her to pray with her underwear on which this discharge has gotten? If it is not permissible, then does she have to repeat her Wudu and change her underwear?
Praise be to Allah.The discussion on such discharges focuses on two issues: 
Are discharges pure or impure? 
The view of Abu Hanifah and Ahmad, and one of the two views narrated from Ash-Shafi`i – which An-Nawawi classed as correct – is that it is pure. This view was also favoured by Shaykh Ibn `Uthaymin, who said in Ash-Sharh Al-Mumti` (1/392): 
“If these discharges come as the result of intimacy, then they are pure, because they are not the waste products of eating and drinking, thus they are not urine. 
The basic principle is that there is no impurity unless there is evidence that something is impure. Because a man is not obliged to wash his penis if he has intercourse with his wife nor to wash his garment if anything gets onto it; if it were impure then the semen, which is pure, would become impure (through contamination with these discharges). (See Al-Majmu`, 1/406 and Al-Mughni, 2/88) 
Based on this, she does not have to wash her underwear or change them if these discharges get on them. 
Is Wudu invalidated because of discharges or not? 
The view of most of the scholars is that this does invalidate Wudu. This is the view favoured by Shaykh Ibn `Uthaymin (may Allah have mercy on him), who said: 
“Anyone who attributes to me the view that this does not invalidate Wudu is not correct. It seems that he understood from my words that it is pure and does not invalidate Wudu.” (Majmu` Fatawa Ash-Shaykh Ibn `Uthaymin, 11/287) 
He (may Allah have mercy on him) also said (11/285): 
With regard to the belief of some women, that (these discharges) do not invalidate Wudu , I do not know of any basis for that except the view of Ibn Hazm. 
But, if a woman experiences this wetness constantly, then she should do Wudu for every prayer after the time for the prayer begins, and it will not matter if this wetness is discharged after that, even if that happens while she is praying. 
Shaykh Ibn Baz (may Allah have mercy on him) said: 
“If the wetness described happens continually , most of the time, then every woman who experiences that must do Wudu for every prayer when the time begins. This is similar to the case of a woman who suffers from Istihadah (irregular vaginal bleeding outside menses) or one who suffers from urinary incontinence .  
But if this wetness only happens sometimes, and is not ongoing, then it comes under the same rulings as urine – when it happens it invalidates purity, even during the prayer.” (Majmu` Fatawa Ibn Baz, 10/130)  
And Allah knows best.