Mark 8:11-12 NLT

11 When the Pharisees heard that Jesus had arrived, they came and started to argue with him. Testing him, they demanded that he show them a miraculous sign from heaven to prove his authority.
12 When he heard this, he sighed deeply in his spirit and said, “Why do these people keep demanding a miraculous sign? I tell you the truth, I will not give this generation any such sign.”