By Allah, I would rather pass a night in wakefulness on the thorns of as-sa`dan (a plant having sharp prickles) or be driven in chains as a prisoner than meet Allah and His Messenger on the Day of Judgement as an oppressor over any person or a usurper of anything out of worldly wealth. And how can I oppress any one for (the sake of a life) that is fast moving towards destruction and is to remain under the earth for a long time?
...
By Allah, even if I am given all the domains of the seven (stars)
with all that exists under the skies in order that I may disobey Allah
to the extent of snatching one grain of barley from an ant I would not
do it. For me your world is lighter than the leaf in the mouth of a
locust that is chewing it. What has `Ali to do with bounties that will
pass away and pleasures that will not last? We seek protection of Allah
from the slip of wisdom and the evils of mistakes, and from Him we seek
succour.
Read the entire sermon of Imam Ali here: sermon 224 of Nahjulbalagh