If a woman’s nifaas ends before forty days, she should do ghusl andpray and fast

My wife gave birth aroundthe 15th of Sha'baan. Is it permissible for
her to pray, fast, do 'umrah, readQur'aan and do all other duties
prescribed in Islam when the nifaas (post-partum bleeding) stops and
she is sure of that, or should she wait for 40 days as some people
say?.
Praise be to Allaah.
The majority of scholars, including the four imams, are of the view
that there is no minimum limit for nifaas. Whenever a woman becomes
pure from nifaas, she has to do ghusl and pray and fast, even if that
is before fortydays have passed since the birth. Because no precise
definition has been narrated in sharee'ah with regard to the minimum
length of nifaas, so the matter should be based on experience, which
shows that nifaas may be very short or it may be long. - Ibn Qudaamah
in al-Mughni, 1/428. Some ofthe scholars narrated that there was
consensus on this point. Al-Tirmidhi (may Allaah have mercy on him)
said: The scholars among the companions ofthe Prophet (peace and
blessings of Allaah be upon him), the Taabi'een and those who came
afterthem are agreed that a woman in nifaas should stop praying for
forty days, unless she sees that she has become pure before that, in
which case she should do ghusl and pray.
See al-Majmoo' by al-Nawawi, 2/541.
Shaykh Ibn Baaz (15/195) was asked: is it permissible for a woman in
nifaas to pray, fast and do Hajj before forty days if she becomes pure
(i.e., ifthe bleeding stops)?
He replied: yes it is permissible for her to fast,pray and do Hajj and
'umrah, and it is permissible for her husband to have intercourse with
her within forty days, if she becomes pure. If she becomes pure after
twenty days, she should do ghusl and pray and fast, and she is
permissible for her husband. The report from 'Uthmaan ibn Abi'l-Aas
which says that he regarded that as makroohis to be understood as
meaning disliked but not forbidden; this is his ijtihaad, but there is
no evidence for that.
The correct view is that there is nothing wrong with that if the woman
becomes pure before forty days. If the bleeding resumes within forty
days, then the correct view is that she should regard it as nifaas
within the forty-day period, but her fasts, prayers and Hajj at the
time when she waspure are still valid and shedoes not have to repeat
any of them, so long as they were done when shewas pure.
It says in Fataawa al-Lajnah al-Daa'imah (5/458):
If a woman in nifaas sees that she has become pure before forty days
are over,then she should do ghusl and pray and fast, and herhusband
may have intercourse with her.
The Standing Committee (10/155) was asked abouta woman who gave birth
seven days before Ramadaan, then she became pure and fasted Ramadaan.
They replied: If the matter is as described and she fasted Ramadaan at
a time whenshe was pure, then her fast is valid and she does not have
to make it up.