Jah-dhamah Radiallahu 'Anha, the wife of Bashir Kha-saasiyyah Radiallahu 'Anhu says:
"I saw Rasulullah Sallallahu 'Alayhi Wasallam coming out of the house after taking a bath and was stroking (or combing) his hair. There were signs of henna on his mubaarak head." (ID)
English reference (ID): Book 6, Hadith 46 (ID)
Arabic reference (ID): Book 6, Hadith 47 (ID)