From Sahih Bukhari (Hadith 5412):
Narrated Sa`d:I was one of (the first) seven (who had embraced Islam) with Allah's Messenger (ﷺ) and we had nothing to eat then, except the leaves of the Habala or Hubula tree, so that our stool used to be similar to that of sheep. Now the tribe of Bani Asad wants to teach me Islam; I would be a loser and all my efforts would be in vain (if I learn Islam anew from them)
Reference: Bukhari 5412