Sahih Muslim Book 6, Hadith Number 2415.
Chapter : Excellence of taking meal before dawn, stress on giving It preference and preference for deferring it (at the fag end of the night) and hastening in breaking it.
Zaid b. Thabit (Allah be pleased with him) said: We took meal shortly before dawn along with the Messenger of Allah (may peace be upon him). We then stood up for prayer. I said: How much span of time was there between the two (acts, i.e. taking of Sahri and observing of prayer)? He said (a span of reciting) fifty verses.