Tirmidhi

14. Commentary:
➊ Day and night are inseparable from each other; therefore, whether one says "day" or "night," it makes no difference.
➋ Forty days is the maximum limit; otherwise, whenever there is a need—meaning if one feels disgust or filth and dirt begin to accumulate—cleanliness may be maintained, whether it concerns hair or nails.

Hadith Commentary:
Vocabulary of the Hadith:
(1)
Nidd:
An equal or a peer,
one of equal standing.
(2)
Halilah:
Wife,
because she stays with her husband and is lawful (halal) for him.

Benefits and Issues:
For any worldly reason—whether it is poverty and hardship or the fear and apprehension of it—preventing the birth of children is, after shirk (associating partners with Allah), the greatest crime, which Muslim governments and individuals are committing by falling prey to the conspiracies of non-Muslims.
(That is, they cooperate with non-Muslim funds, etc., for birth control,
while in their own countries, they exempt taxes for having more children.)
And a person is the guardian of his neighbor’s honor and dignity;
if he himself begins to violate that honor or tries to lead his neighbor astray,
then this is like the fence itself eating the crop,
therefore, it has been declared an extremely abhorrent and grave crime.

Explanation:
1:
The meaning is that it should not exceed forty days;
this does not mean that it is not permissible within forty days.

Benefit:
Whenever the need is felt, these acts should be performed; however, if there is a delay, it should not exceed forty days, otherwise one will be sinful.
It should not be assumed that cleanliness should not be maintained before forty days.