If a menstrual period lasts longer than usual

If the period lasts longer than usual, the correct thing is
to follow what is usual. If her period is usually five days, but this time
it is six or seven or eight, the right thing to do is to refrain (from
praying etc) so long as the blood is flowing, and regard it as menses, and
not pray or fast, and it is not permissible for her husband to have
intercourse with her in this case, because the period may be longer or
shorter; this is normal among women. But if she bleeds for longer, she
should not pray and fast, and if it is shorter and she sees that the
period has ended, she should do ghusl and she becomes permissible for her
husband, and she should pray and fast. This is the correct response in
this case. 

But if she becomes pure and does ghusl, then she sees
yellowish or brownish discharge, this yellowish or brownish discharge is not
regarded as anything (i.e., is not menses), so she should pray and fast, as
Umm ‘Atiyyah (may Allah be pleased with her) said: We used not to regard the
brownish or yellowish discharge that comes after tuhr (becoming pure) as
being of any significance. 

If she does ghusl after her period, then sees yellowish or
brownish discharge, this does not count as anything or prevent her from
praying or fasting or having intercourse with her husband. But in the case
of pure blood that is clearly blood, then she should stop praying etc., even
is it was interrupted. Whether it is continuous or interrupted, she should
stop praying etc. according to her regular cycle. End quote. 

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him)