There are numerous examples of explanation of the Qur'an by the Prophet, who either himself asked the Angel Gabriel for explanation of matters not clear to him, or who was asked by the Companions about the Qur'an. Suyuti has given a long list of explanations of the Qur'an by the Prophet sura by sura. [Itqan, 11, pp. 191-205.]

Here one example may suffice:

'And eat and drink until the white thread of dawn appears to you distinct from its black thread. . .' (2: 187).

Narrated 'Adi b. Hatim: I said: 'O Allah's Apostle! What is the meaning of the white thread distinct from the black thread? Are these two threads?' He said: 'You are not intelligent, if you watch the two threads'. He then added, 'No, it is the darkness of the night and the whiteness of the day'. [Itqan 11. pp. 191-205.]