What is the main topic of Bulugh al-Maram Hadith 154?

Bulugh al-Maram Hadith 154 is from chapter "The Book of Purification". Summary: and Al-Bukhari said, "It is the most authentic in this chapter" .

Bulugh al-Maram: Hadith 154

1. The Book of Purification

1/10 Chapter:

باب الحيض

154

Bulugh al-Maram

وَقَالَ اَلْبُخَارِيُّ: هُوَ أَصَحُّ شَيْءٍ فِي هَذَا اَلْبَابِ.‏

and Al-Bukhari said, "It is the most authentic in this chapter" .

Reference: Bulugh al-Maram 73
In-book : Book 1, Hadith 88
English translation : Book 1, Hadith 79