From Sahih Bukhari (Hadith 3874):
Narrated Um Khalid bint Khalid:When I came from Ethiopia (to Medina), I was a young girl. Allah's Messenger (ﷺ) made me wear a sheet having marks on it. Allah's Messenger (ﷺ) was rubbing those marks with his hands saying, "Sanah! Sanah!" (i.e. good, good)
Reference: Bukhari 3874