It is narrated from Imam Ali (AS) who said:

Patience is the fruit of certainty, and patience is the result of belief [1]. One day Imam Ali (AS) was passing a meat shop and the butcher told him: O’ Amiral Momeneen, I have brought lots of very good quality meat, if you want take some. Imam Ali (AS) said: I do not have money now to buy some meat. The butcher said: I will wait, you can pay later. Imam (AS) said: I tell my stomach to wait. If I could not tell my stomach to wait, I would have asked you to wait; but now that I can, I say to my stomach to wait [2].

[1] Qorarul Hekam, Vol. 1, Page 606.

[2] Hekayat’ha va Hedayat’ha, Page 107.

Source: en.shafaqna.com