From Sahih Bukhari (Hadith 1523):
Narrated Ibn `Abbas:The people of Yemen used to come for Hajj and used not to bring enough provisions with them and used to say that they depend on Allah. On their arrival in Medina they used to beg the people, and so Allah revealed, "And take a provision (with you) for the journey, but the best provision is the fear of Allah
Reference: Bukhari 1523