Hadith: A time limit was set for us regarding trimming the mustache, clipping the nails, plucking the armpit hair, and shaving the pubic hair—that we should not leave them for more than forty nights

عَنْ أَنَسِ بْنِ مَالِكٍ رَضيَ اللهُ عنهُ قَالَ:
وُقِّتَ لَنَا فِي قَصِّ الشَّارِبِ، وَتَقْلِيمِ الْأَظْفَارِ، وَنَتْفِ الْإِبِطِ، وَحَلْقِ الْعَانَةِ، أَلَّا نَتْرُكَ أَكْثَرَ مِنْ أَرْبَعِينَ لَيْلَةً.
[صحيح] - [رواه مسلم] - [صحيح مسلم: 258]

Anas ibn Mālik (may Allah be pleased with him) reported:
A time limit was set for us regarding trimming the mustache, clipping the nails, plucking the armpit hair, and shaving the pubic hair—that we should not leave them for more than forty nights.
[Authentic hadith] - [Narrated by Muslim] - [Sahih Muslim - 258]

Explanation

The Prophet (may Allah's peace and blessings be upon him) specified that trimming a man's mustache, cutting the fingernails and toenails, plucking the armpit hair, and shaving the pubic hair should not be neglected for more than forty days.

Benefits from the Hadith

1. Ash-Shawkāni said: The preferred view is that it should be within the forty days specified by the Messenger of Allah (may Allah's peace and blessings be upon him), and it is not permissible to exceed this period. However, one is not considered to be opposing the Sunnah if he delays the trimming and the like after it has grown, as long as it does not surpass this limit.
2. Ibn Hubayrah said: This Hadīth represents the maximum limit for delaying these things, and it is preferable to attend to them before reaching this limit.
3. Islam assigns good care to cleanliness, purification, and adornment.
4. Trimming the mustache is done by removing some of the hair growing on the upper lip.
5. Plucking the armpit hair is done by removing the hair that grows there, which is the area beneath the joint connecting the arm to the shoulder.
6. Shaving the pubic hair, which is the coarse hair that grows around the private parts, for both men and women.