Sahih Muslim Book 4, Hadith Number 1301.

Chapter : Desirability of observing the noon prayer at the earlier hour (of times prescribed for it) when there is no intense heat.

‘Ala’ b. ‘Abd al-Rahman reported that they came to the house of Anas b. Malik in Basra after saying the noon prayer. His (Anas) house was situated by the side of the mosque. As revisited him he (Anas) said: Have you said the afternoon prayer? We said to him: It is just a few minutes before that we finished the noon prayer. He said: Offer the afternoon prayer. So we stood up and said our prayer. And when we completed it, he said: I have heard the Messenger of Allah (may peace be upon him) saying: This is how the hypocrite prays: he sits watching the sun, and when it is between the horns of devil, he rises and strikes the ground four times (in haste) mentioning Allah a little during it.