Buddha verifying his enlightenment If I remember correctly, Buddha wanted to verify his insight after his sit under the Bodhi tree. He took a leaf and reversed the cause-and-effect leading to him holding that leaf in order to check something. Can anyone point to the story?
In the case of Gauthama the Buddha, there is no description about a leaf. The Buddha did review dependent origination, direct, reverses and direct &amp; reverse order, as in the other answers.

But there are cases of Pacceka Buddha's who have been enlightened by seeing a withered leaf.


  Two other Jātaka tales report the attainment of Paccekabodhi on seeing a
  withered leaf fall. In these cases, too, it is clearly an external condition
  that is responsible for the break-through to awakening. 


Paccekabuddhas in the Isigili-sutta and its Ekottarika-āgama Parallel Bhikkhu Anālayo 


  At that instant Darīmukha seeing the garden now empty came and sat on the royal seat in the garden. A withered leaf fell before him. In it he came to see the principles of decay and death, grasped the three marks of things, and making the earth re-echo with joy he entered on paccekabodhi.


No. 378. DARĪMUKHA-JĀTAKA. The Jataka Volume III tr. by H.T. Francis and R.A. Neil ed. E. B. Cowell [1897]


  But when the king was gone, Sonaka returned and sat on the stone seat, and so it was that a withered leaf of a sāl tree fell from its stalk in front of him, and on seeing it he cried, "Even as this leaf, so will my body fall into decay," and acquiring supernatural insight by reflecting on the impermanence of all things he attained to the state of a paccekabuddha, and at this very instant his characteristic as a layman vanished, and the marks of an ascetic became visible, and saying, "There is no more re-birth for me," in the utterance of this aspiration he set out for the cave of Nandamūla.


No. 529. SONAKA-JĀTAKA. The Jataka Volume V tr. by H.T. Francis and R.A. Neil ed. E. B. Cowell [1905]