From Sahih Muslim (Hadith 2552):
Zaid b. Thabit (Allah be pleased with him) said:We took meal shortly before dawn along with the Messenger of Allah (ﷺ). 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
Reference: Muslim 2552