from the Prophet ﷺ, that he ﷺ fixed the time as every forty nights for them to trimming the fingernails, taking from the mustache, and shaving the pubic hairs.  

عَنِ النَّبِيِّ ﷺ أَنَّهُ وَقَّتَ لَهُمْ فِي كُلِّ أَرْبَعِينَ لَيْلَةً تَقْلِيمَ الأَظْفَارِ وَأَخْذَ الشَّارِبِ وَحَلْقَ الْعَانَةِ  

"[The Messenger of Allah ﷺ] fixed the time for us paring the mustache, trimming the fingernails, shaving the pubic hairs and plucking the underarm hairs - that we not leave it for more than forty days."  

وَقَّتَ لَنَا رَسُولُ اللَّهِ ﷺ فِي قَصِّ الشَّارِبِ وَتَقْلِيمِ الأَظْفَارِ وَحَلْقِ الْعَانَةِ وَنَتْفِ الإِبْطِ أَنْ لاَ نَتْرُكَ أَكْثَرَ مِنْ أَرْبَعِينَ يَوْمًا قَالَ هَذَا أَصَحُّ مِنْ حَدِيثِ الأَوَّلِ وَصَدَقَةُ بْنُ مُوسَى لَيْسَ عِنْدَهُمْ بِالْحَافِظِ