Bukhari

Hadith Commentary:
➊
The ahadith mentioned under this heading describe the method of washing menstrual blood, stating that one should be thorough in purifying the garment from blood.
This is done by first pouring a little water and rubbing with the fingertips, then washing it, and after that, it is permissible to pray in that same garment.
The benefit of rubbing with the fingertips is that the blood which has become embedded in the threads of the cloth will be removed.
The purpose is that when washing menstrual blood, one should be very thorough.

➋
Imam al-Bukhari rahimahullah established a chapter in the Book of Ablution (Kitab al-Wudu’) with the following words:
“Chapter: Washing Blood,” in which he discussed washing all types of blood, and then he mentioned the washing of semen (mani), stating that due to its common occurrence, there was some leniency in washing it.
From this, someone might think that there is also leniency in washing menstrual blood, so to remove this notion, it is stated:
Special care is required in washing it.
There is consensus (ijma‘) on the impurity (najasah) of menstrual blood. At the end of this hadith, it is mentioned that then water should be poured over the entire garment; Hafiz Ibn Hajar rahimahullah has considered this to be for the removal of doubts and misgivings (waswasah).
(Fath al-Bari: 1/532)
In the previous hadith, the washing of istihada blood (non-menstrual bleeding) was discussed; here, clarification is given regarding menstrual blood.
To make the distinction clear, it is stated that menstrual blood should be washed thoroughly, whereas for istihada blood, such effort is not necessary.
The second difference will be mentioned in the next chapter: a menstruating woman (ha’idh) cannot enter the mosque, whereas a woman experiencing istihada (mustahada) can even perform i‘tikaf in the mosque.
From this, it is understood that the impurity of istihada blood is somewhat lighter compared to menstrual blood.
And Allah knows best.