Luke 17: 5 - 10
5 The apostles said to the Lord, "Increase our faith!"
6 And the Lord said, "If you had faith as a grain of mustard seed, you could say to this sycamine tree, `Be rooted up, and be planted in the sea,' and it would obey you.
7 "Will any one of you, who has a servant plowing or keeping sheep, say to him when he has come in from the field, `Come at once and sit down at table'?
8 Will he not rather say to him, `Prepare supper for me, and gird yourself and serve me, till I eat and drink; and afterward you shall eat and drink'?
9 Does he thank the servant because he did what was commanded?
10 So you also, when you have done all that is commanded you, say, `We are unworthy servants; we have only done what was our duty.'"

EWTN