Sunan an Nasai
2155
Sahih+2

Hisam reported from Qatadah, from Anas, that Zaid bin Thabir said; "We took Sahur with the Messenger of Allah then we went to pray." I said:"How long was there between them?" He said: "As long as it takes a man to recite fifty verses

SahihAbu Ghuddah
SahihAl-Albani