Letter of James 4:13-17.
Beloved : Come now, you who say, “Today or tomorrow we shall go into such and such a town, spend a year there doing business, and make a profit”–
you have no idea what your life will be like tomorrow. You are a puff of smoke that appears briefly and then disappears.
Instead you should say, “If the Lord wills it, we shall live to do this or that.”
But now you are boasting in your arrogance. All such boasting is evil.
So for one who knows the right thing to do and does not do it, it is a sin.