Ibn 'Abbaas Radiyallahu 'Anhu reports:
"Rasulullah Sallallahu 'Alayhi Wasallam applied kuhl of ithmid three times in each eye before sleeping'. In a narration also from Ibn 'Abbaas Radiyallahu 'Anhu, it is reported: "Rasuluilah Sallallahu'Alayhi Wasallam had a small container for keeping kuhl, from which he applied in each eye kuhl three times before sleeping'. (FR)
English reference (FR): Book 7, Hadith 49 (FR)
Arabic reference (FR): Book 7, Hadith 50 (FR)