31 He put another parable before them, saying, “The kingdom of heaven is like a grain of mustard seed that a man took and sowed in his field. 32 It is the smallest of all seeds, but when it has grown it is larger than all the garden plants and becomes a tree, so that the birds of the air come and make nests in its branches.”
11:1 Now faith is the assurance of things hoped for, the conviction of things not seen. 2 For by it the people of old received their commendation. 3 By faith we understand that the universe was created by the word of God, so that what is seen was not made out of things that are visible.
18 In hope he believed against hope, that he should become the father of many nations, as he had been told, “So shall your offspring be.” 19 He did not weaken in faith when he considered his own body, which was as good as dead (since he was about a hundred years old), or when he considered the barrenness of Sarah's womb. 20 No distrust made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, 21 fully convinced that God was able to do what he had promised.
20 He said to them, “Because of your little faith. For truly, I say to you, if you have faith like a grain of mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move, and nothing will be impossible for you.”  (ESV)
 17:20 Some manuscripts insert verse 21: But this kind never comes out except by prayer and fasting