“Jesus answered them.
He said to them.
καὶ ἀποκριθεὶς ὁ Ἰησοῦς λέγει αὐτοῖς Ἔχετε πίστιν θεοῦ.
This is somewhat similar to Matthew, chapter 21:21. However, Mark is more succinct here. Jesus answered the disciple’s question or Peter’s remark (καὶ ἀποκριθεὶς ὁ Ἰησοῦς) about how the fig tree withered. He merely said to them (λέγει αὐτοῖς) to have faith in God (Ἔχετε πίστιν θεοῦ).