Sahih Muslim Book 6, Hadith Number 2405.

This Hadith has been narrated by Sulaiman al-Taimi with the same chain of transmitters (but with a slight variation of words) that he (the Holy Prophet) said: The dawn is not like it as it is said; he then gathered his fingers and lowered them. But he said, it is like this (and he placed the index finger upon the other one and spread his hand).