Shama-il Tirmidhi Chapter 047, Hadith Number 010 (335).

Jaabir Radiyallahu 'Anhu says. "Rasulullah Sallallahu 'Alayhi Wasallam never said 'No' to a request of a person".

Commentary
If he was in possession of the required article at that moment, he gave it, otherwise he would promise to give it at another time, or he would make du'aa for the person, that Allah fulfil the person's need by some other means.