The Cow - 2:265
The example of those who spend their money because they want to earn Allah´s pleasure and they are convinced of it is like the example of a high-yielding garden which yields double its produce when it receives abundant rain, and is content with the dew even if it does not receive abundant rain. Allah sees what you do.
Related:
The Cow/2:261
The example of those who spend their money in the Way of Allah is like that of a grain which yields seven ears of grain, one hundred in each. Allah gives in multiples to whomever He wills. Allah is Generous, Knowing.
The Heights/7:58
The good land produces crops by the permission of your Lord. But the bad land does not yield anything useful. Thus do We make clear the verses for a grateful people.