Is it obligatory to ascertain purity from menstruation using a piece of cloth or cotton, or is it sufficient to be certain of purity by any other means, such as no blood descending for 24 hours?

The signs of a woman's purification from menstruation are dryness (by the cessation of blood, yellowness, and turbidity) or the white discharge (a fluid resembling lime). Many women do not see the white discharge, and dryness is sufficient to deem her pure.

To ensure the end of menstruation, one must ascertain this at the end of the usual menstrual period by inserting a piece of cotton or similar material. It is not sufficient to merely wait and perform ghusl (ritual bath) without ensuring purity, so as not to miss obligatory prayers and fasting, or to render the ghusl invalid.

Some scholars are of the opinion that a woman is not obligated to check for her purity in the middle of the night; rather, this should be done close to the time of prayer, i.e., before sleep and before the Fajr prayer.