What is the ruling on the yellow discharge that appears after purification from menstruation, which may resemble egg yolk after exposure to air, and is it obligatory to check the cotton (panty liner/pad) before every prayer, given the presence of pure discharges most of the time, knowing that this checking invalidates ablution?

Yellow discharge is impure (najis); one must perform istinjāʾ (washing of the private parts) from it. However, one is not required to inspect or search for it. But if you are certain of its emission, then you must perform istinjāʾ and wuḍūʾ (ablution) for prayer. If you are in doubt, you may act upon the original presumption, which is that nothing has exited. If its emission is continuous, then your ruling is that of one afflicted with salas (incontinence): you perform wuḍūʾ for each prayer after its time has begun, and you may pray with that wuḍūʾ as many obligatory and supererogatory prayers as you wish until that time expires. Yellow secretions are ruled to be impure, whereas pure discharges are the normal white ones.