Nasai

Since generally marriage (nikah) is conducted only after the completion of postnatal bleeding (nifas), and moreover, the full benefits of marriage are attained at that time, this is why it was stated as such. Otherwise, it does not mean that marriage cannot take place during nifas. There is nothing that prevents marriage during the period of nifas. The waiting period (‘iddah) was until childbirth, which has now ended. This matter becomes clearly understood from the detailed narration. See: Hadith: 3540, 3541.

Hadith Commentary:
Qur’ (قرء) comes in the meaning of both menstruation (hayd) and purity (tuhr).
That is why Imam Abu Hanifah rahimahullah has taken “thalathata quroo’” (three qur’) to mean three menstruations, while al-Shafi’i has taken it to mean three periods of purity.
However, the madhhab of Imam Abu Hanifah rahimahullah is more correct, because divorce (talaq) is legislated during a period of purity (tuhr), not during menstruation (hayd). Now, if someone gives divorce during one period of purity, then either this period of purity will be counted in the waiting period (‘iddah),
The Shafi’is say: In that case, the ‘iddah will be less than three periods of purity.
If it is not counted, then the ‘iddah will become more than three periods of purity.
The Shafi’is answer this by saying that two periods of purity and a part of the third period of purity can be called “three periods of purity,” just as Allah says:
﴿الْحَجُّ أَشْهُرٌ مَعْلُومَاتٌ﴾ () (al-Baqarah: 197),
even though in reality, the months of Hajj are two months and ten days.

Hadith Commentary:
(1)
In the noble verse, the waiting period (‘iddah) for a pregnant woman is stated: if she is divorced, then after delivering the child, she may marry elsewhere.
If her husband has passed away while she is pregnant, then her waiting period is also until delivery.
The position of Ibn Abbas (radi Allahu anhuma) is that if a woman is pregnant at the time of her husband’s death, she must observe the longer period as her ‘iddah. However, the rest of the noble Companions (radi Allahu anhum) hold the opposite view, because Surah at-Talaq, in which the ‘iddah of a pregnant woman is mentioned, was revealed after Surah al-Baqarah, in which the ‘iddah of a woman whose husband has died is mentioned.

(2)
It should be noted that Ibn Abbas (radi Allahu anhuma) used to present as evidence the verse 234 of Surah al-Baqarah, that a woman whose husband dies while she is pregnant should complete the last term.
Abu Salamah said to Ibn Abbas (radi Allahu anhuma):
Did Allah, the Exalted, not say “the last of the two terms”?
If, after the husband’s death, four months and ten days pass and she has not delivered the child, can she marry? Upon hearing this, Ibn Abbas (radi Allahu anhuma) said to his servant:
Go and ask Umm Salamah (radi Allahu anha) about this.
In any case, the waiting period (‘iddah) for a pregnant woman is until delivery, whether her husband has died or she has been divorced.
And Allah knows best. (Fath al-Bari: 9/573)

If a woman's husband passes away and she is pregnant, then according to the majority of scholars, her waiting period (‘iddah) is not four months and ten days, but rather until she gives birth (delivery of the child). When the child is born, she is free; if she wishes, she may remarry. At this point, mourning (ḥidad) is also no longer obligatory for her, but until her postnatal bleeding (nifas) ends, her husband cannot approach her. Ibn Abbas (radi Allahu anhu) was of the opinion that the longer of the two waiting periods applies—that is, if the child is born before four months and ten days, then the waiting period is four months and ten days, and if four months and ten days pass before the child is born, then the waiting period is until the child is born. In other words, he believed that mourning is necessary in its own right, and the delivery of the child is necessary in its own right. He acted upon both the hadiths and the Qur’anic verse simultaneously. Although this view is reasonable, it is contrary to the aforementioned hadith; therefore, it is not considered valid.

Takhrij:
«أخرجه البخاري، الطلاق، باب : ﴿وأولات الأحمال أجلهن أن يضعن حملهن﴾، حديث:5320، ومسلم، الطلاق، باب انقضاء عدة المتوفي عنها وغيرها بوضع الحمل، حديث:1485، وانظر، حديث:1484.»©Explanation:
This hadith establishes that if a woman's husband passes away and she is pregnant, then her waiting period (‘iddah) is until the delivery of the child—that is, her ‘iddah ends as soon as she gives birth, whether this period is less than or more than four months and ten days. As in the case of Sayyidah Subay‘ah radi Allahu anha, when she gave birth to her child approximately forty days after her husband's death, the Messenger of Allah sallallahu alayhi wa sallam permitted her to remarry.

This is the opinion of the majority of scholars.

Their primary evidence is the statement of Allah, the Exalted: ﴿ وَأُولَاتُ الْأَحْمَالِ أَجَلُهُنَّ أَنْ يَضَعْنَ حَمْلَهُنَّ ﴾ “The waiting period of pregnant women is until they deliver their burden (i.e., give birth).”
In this verse, just as the ‘iddah of a pregnant divorcee is mentioned, so too is the ‘iddah of a pregnant widow, as is also explicitly stated from the Messenger of Allah sallallahu alayhi wa sallam, which Imam Abdullah ibn Ahmad has narrated in the Zawa’id of the Musnad, and Diya’ has narrated in al-Mukhtarah.

Clarification: «حضرت سُبَیْعَہ رضی اللہ عنہا » (with diminutive form) bint Harith Aslamiyyah.
She is called Aslamiyyah due to her attribution to the tribe of Banu Aslam.
She is a well-known and renowned female Companion (sahabiyyah).
According to Ibn Sa‘d, she was among the Emigrants (muhajirat).
She was married to Sa‘d ibn Khawlah radi Allahu anhu, who passed away in Makkah during the Farewell Pilgrimage (Hajjat al-Wada‘). Afterwards, she married a young man from her tribe.
Some have mentioned that she married the well-known Companion Abu Sanabil radi Allahu anhu.

«امام زہری رحمہ اللہ » Muhammad ibn Muslim ibn ‘Ubaydullah ibn ‘Abdullah ibn Shihab al-Qurashi al-Zuhri.
He was a great Imam.
He was a scholar of the Hijaz and al-Sham.
He was among the prominent scholars of the fourth generation.
Everyone is agreed upon his eminence and precision.
Imam Layth said: I have never seen a scholar as comprehensive in qualities as Ibn Shihab.
And Imam Malik rahimahullah said that Ibn Shihab was a very generous person; among people, his like and equal cannot be found.
He passed away in 124 AH.