Praise be to Allaah.
If a woman who is in nifaas (i.e., bleeding following
childbirth) sees al-tuhr (end of bleeding) before forty days had passed, she
should do ghusl and pray and fast. The tuhr – following menstruation or
nifaas – is recognised by one of two signs:
Complete dryness, in the sense
that there is no trace of blood, or yellowish or brownish discharge.
Al-Nawawi (may Allah have mercy on him) said: The sign that
menses has ended and tuhr (purity) has begun is the cessation of bleeding
and of yellowish and brownish discharge. If it stops, then the woman has
become pure, regardless of whether any white discharge comes after that or
End quote from al-Majmoo‘, 2/562
If in the case asked about the bleeding had stopped, and
there was no longer any trace of it or any yellowish or brownish discharge,
that this was the sign of tuhr (i.e., she had become pure), and her fast is
valid in that case, and it does not matter if there was any white discharge,
because that is normal secretion from the vagina.
For more information please see the answers to questions no.
And Allah knows best.