'Umar Radiyallahu 'Anhu reports that once a needy person came to ask Rasulullah Sallallahu 'Alayhi Wasallam for his need. Rasulullah Sallallahu 'Alayhi Wasallam replied:
"I do not have anything at present. Go and purchase something on my behalf. When something arrives I will pay for it". 'Umar Radiyallahu 'Anhu said: "O Messenger of Allah, whatever you possessed you have already given away. Allah Ta'aala did not make you responsible for that which is not in your means". Rasulullah Sallallahu 'Alayhi Wasallam felt annoyed at this saying of 'Umar Radiyallahu'Anhu. Thereupon a person from among, the Ansaar said: "O Rasul, of Allah, spend whatever you wish, and do not fear any lessening from the Lord of the 'Arsh (Throne)". (That Great Deity that is the Lord of the 'Arsh, nothing will decrease in His Bounties by giving you). Rasulullah Sallallahu 'Alayhi Wasallam smiled and the happiness could be seen on his mubaarak face due to the saying of the Ansaari. Rasulullah Sallallahu 'Alayhi Wasallam than said: "Allah Ta'aala has commanded me to do this".
English reference: Book 47, Hadith 338
Arabic reference: Book 48, Hadith 355