Therefore, being sincere is the way of heaven; being sincere is the way of man.

From:

Chapter 12 of "Mencius Li Lou Shang"

Mencius said: If you live in a lower position and do not gain access to those above, you will not be able to govern the people. also. There is a way to gain from superiors: If you don’t trust your friends, you won’t gain from superiors. There's a way to trust your friends: it's not a pleasure to do things with relatives, it's not a good idea to trust your friends. There is a way to please relatives: If you are not sincere, you will not be happy with relatives. There is a way to be sincere to one's body: if one does not know what is good, one will not be sincere to one's body. Therefore, being sincere is the way of heaven; being sincere is the way of man. If you are sincere and do not move, you have not yet existed; if you are not sincere, you have not moved.