Shama-il Tirmidhi Chapter 35, Hadith Number 1 (225).

Anas ibn Maalik radiyallahu anhu relates, Rasoolullah sallallahu alaihe wasallam once told him jokingly, Ya dhal udhu-nayn (O two eared one).

Commentary
Every person has two ears. It must have been for a special reason that he was called Ya dhal udhu-nayn For example, he might have had large ears or a sharp hearing, that he could hear from a distance. The latter explanation seems more correct.