ينبغي أن تكون أفعال الرجل أحسن من أقواله و لا تكون أقواله أحسن من أفعاله
A person’s deeds must be better than his words, a person’s words must not be better than his deeds.
This is equivalent to the English saying: deeds, not words. And also: Actions speak louder than words.
In the context of religion, this quote tells us that we have to perform its duties rather than just deliver its sermons. And in the context of worldly pursuits, it tells us the importance of walking the talk.