Midrasch zu Bereschit 23:11

R. Huna had wine in a room which was in an unsafe condition, and the walls of which were momentarily expected to fall. He wished to remove the wine, [but was afraid to enter the room]. So he got R. Ada b. Ahaba to enter the room with him and engaged him there in a discussion of an Halacha, until his men removed the wine. After they had left, the walls of the room caved in. When R. Ada realized how he had been used, he became angry, for he agreed with R. Janai, who said: "A man should never expose himself to danger expecting that a miracle will be wrought for him; for it may be that such a miracle will not be wrought, and even if a miracle be wrought for him, it will be deducted from the rewards due him for his merits." R. Chanin said: "What is the Biblical passage for this? (Gen. 23, 11) I am not worthy of all the kindness, etc." Wherein lay the greatness of Ada b. Ahaba? As we are taught: The disciples of R. Ada b. Ahaba asked him: "Why have you lived so long?" He replied: "I was never angry in my house; I never superseded a superior; I never thought of Divine subjects in unclean alleys; I never walked four cubits without studying the Torah or without Phylacteries; I never slept in the house of study, neither regularly nor took a nap; I never rejoiced when my neighbor was in misfortune, and I never called my fellow man by a nickname."

Whence do we know that the wicked say much but do not do even a little? We find this illustrated by Ephron, who at first said to Abraham: The field I give thee, and the cave that is therein I give thee (Gen. 23:11), only to declare later: The land is worth four hundred shekels of silver, what is that betwixt me and thee? (ibid., v. 15), which it was not worth.