Fadhl Ibn Abi Qarrah relates:
Once when we approached Imam Sadiq (peace be upon him), we found him hard at work in his field. Observing this, we said to him (peace be upon him): May we be made your ransom! Either permit us to do the work or let your servants do it.
The Imam (peace be upon him) said: No. Let me work. I desire that I meet God after having exerted myself and worked by my own hands in seeking lawful sustenance.
He (peace be upon him) then added: Even Ali (peace be upon him) used to inconvenience himself for the purpose of procuring lawful income.( Shanidani-ha-e-Taareekh, pg. 47; Mahajjah al-Baidhaa, vol. 3, pg. 147. )