خصال الفطرة
Five grooming and hygiene practices described as part of natural human disposition: trimming the mustache, letting the beard grow, using the tooth-stick, cutting the nails, and washing the finger joints.
خَمْسٌ مِنَ الْفِطْرَةِ: الْخِتَانُ، وَالِاسْتِحْدَادُ، وَقَصُّ الشَّارِبِ، وَتَقْلِيمُ الْأَظْفَارِ، وَنَتْفُ الْإِبِطِ
“Five things are part of natural disposition: circumcision, shaving pubic hair, trimming the mustache, clipping the nails, and plucking the underarm hair.” (meaning, not a literal translation)
Classical physicians grouped these under general bodily hygiene — reducing sites where bacteria and odor accumulate, well before germ theory offered a mechanism.