Sunan Ibn Majah, Book 1, Hadith 311 (In-Book) ⓘ

It was narrated that Anas bin Malik said: "We were given a time limit with regard to trimming the mustache, shaving the pubic hairs, plucking the armpit hairs and clipping the nails. We were not to leave that for more than forty days."

حَدَّثَنَا بِشْرُ بْنُ هِلاَلٍ الصَّوَّافُ، حَدَّثَنَا جَعْفَرُ بْنُ سُلَيْمَانَ، عَنْ أَبِي عِمْرَانَ الْجَوْنِيِّ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ وُقِّتَ لَنَا فِي قَصِّ الشَّارِبِ وَحَلْقِ الْعَانَةِ وَنَتْفِ الإِبْطِ وَتَقْلِيمِ الأَظْفَارِ أَنْ لاَ نَتْرُكَ أَكْثَرَ مِنْ أَرْبَعِينَ لَيْلَةً ‏.‏