Matthew 12:39
37 For by your words you will be justified, and by your words you will be condemned.” 38 Then some of the experts in the law along with some Pharisees answered him, “Teacher, we want to see a sign from you.” 39 But he answered them, “An evil and adulterous generation asks for a sign, but no sign will be given to it except the sign of the prophet Jonah. 40 For just as Jonah was in the belly of the huge fish for three days and three nights, so the Son of Man will be in the heart of the earth for three days and three nights. 41 The people of Nineveh will stand up at the judgment with this generation and condemn it because they repented when Jonah preached to them—and now, something greater than Jonah is here!
Sanhedrin 98a
Babylonian Talmud§ Rabbi Yosei ben Kisma’s students asked him: When will the son of David come? Rabbi Yosei ben Kisma said: I am hesitant to answer you, lest you request from me a sign to corroborate my statement. They said to him: We are not asking you for a sign. Rabbi Yosei ben Kisma said to them: You will see when this existing gate of Rome falls and will be rebuilt, and will fall a second time and will be rebuilt, and will fall a third time. And they will not manage to rebuild it until the son of David comes. The students said to him: Our rabbi, give us a sign. Rabbi Yosei ben Kisma said to them: But didn’t you say to me that you are not asking me for a sign?
Notes and References
"... many say Matthew has pruned the expression because in his day, unlike the days of Jesus' ministry, only the Pharisees, understood to represent the rabbis, constituted any real opposition. Here, however, the roles are reversed: Mark (8:11) has 'Pharisees'; Matthew (12:38) mentions 'Pharisees and teachers of the law.' Such changes are of little use in establishing Matthew's life-setting. The Jewish leaders phrased their question respectfully ("Teacher"; see on 8:19) and asked for a "sign" (semeion), not just for another miracle. Jesus had already done many miracles. Old Testament and intertestamental Jewish literature shed light on the request (compare K.H. Rengstorf, TDNT, 7:208--21, 225-29; F.J. Helfmeyer, TDOT, 1:167-88; and 1 Samuel 2:30-33; 1 Kings 20:1-14; Isaiah 7:10-25; b Sanhedrin 98a; b Baba Metzia 59b; compare O. Linton, 'The Demand for a Sign from Heaven [Mk.8,11-12 and Parallels],' ST 19 [1965]). A 'sign' was usually some miraculous token to be fulfilled quickly, or at once, to confirm a prophecy ..."
Gaebelein, Frank Ely The Expositor’s Bible Commentary: Matthew, Mark, Luke (p. 294) Pickering & Inglis, 1984