There are two instances in Matthew where the scribes and Pharisees asked Jesus for a sign. These are found in Matt 12 and Matt 16.
Matthew 12:38-40 (NASB)
38 Then some of the scribes and Pharisees said to Him, “Teacher, we want to see a sign from You.”
39 But He answered and said to them, “An evil and adulterous generation craves for a sign; and yet no sign will be given to it but the sign of Jonah the prophet;
40 for just as JONAH WAS THREE DAYS AND THREE NIGHTS IN THE BELLY OF THE SEA MONSTER, so will the Son of Man be three days and three nights in the heart of the earth.
Matthew 16:1-4 (NASB)
1 The Pharisees and Sadducees came up, and testing Jesus, they asked Him to show them a sign from heaven.
2 But He replied to them, “When it is evening, you say, ‘It will be fair weather, for the sky is red.’
3 “And in the morning, ‘There will be a storm today, for the sky is red and threatening.’ Do you know how to discern the appearance of the sky, but cannot discern the signs of the times?
4 “An evil and adulterous generation seeks after a sign; and a sign will not be given it, except the sign of Jonah.” And He left them and went away.
If I’m really honest with myself and God, I often pray my petitions for myself and others wishing that God will perform a miracle in order for me to have a sign that will increase my faith.
Jesus tells us that He has already given us the only sign that we will ever need. His resurrection is the only miracle that is required to have faith in Him. His death paid the price to cover my sins, so that I can be His child and commune with Him through prayer.
And so, I can pray confidently, without a need for another sign or a miracle. I can pray always seeking His will alone, not mine. I can pray earnestly as David did in Psalm 19.
Psalm 19:14 (NASB)
14 Let the words of my mouth and the meditation of my heart Be acceptable in Your sight, O LORD, my rock and my Redeemer.
Always praying for the glory of God,