Al-Kāfi - Volume 6 > The Under arms
Hadith #6

مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ مَحْبُوبٍ عَنْ يُونُسَ بْنِ يَعْقُوبَ أَنَّ أَبَا عَبْدِ اللَّهِ ( عليه السلام ) كَانَ يَدْخُلُ الْحَمَّامَ فَيَطْلِي إِبْطَهُ وَحْدَهُ إِذَا احْتَاجَ إِلَى ذَلِكَ وَحْدَهُ .

6. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ibn Mahbub from Yunus ibn Ya‘qub who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, whenever needed would go to the bathhouse only to apply lime paste to his underarms.’”