Sunan an-Nasa'i 2156
It was narrated from Anas that Zaid bin Thabit said:
"We had Sahur with the Messenger of Allah then we went to pray." I (one of the narrators) said: "It is claimed that Anas said: 'How long was there between them?' He said: 'As long as it takes a man to recite fifty verses."
أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا هِشَامٌ، قَالَ حَدَّثَنَا قَتَادَةُ، عَنْ أَنَسٍ، عَنْ زَيْدِ بْنِ ثَابِتٍ، قَالَ تَسَحَّرْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم ثُمَّ قُمْنَا إِلَى الصَّلاَةِ ‏.‏ قُلْتُ زُعِمَ أَنَّ أَنَسًا الْقَائِلُ مَا كَانَ بَيْنَ ذَلِكَ قَالَ قَدْرَ مَا يَقْرَأُ الرَّجُلُ خَمْسِينَ آيَةً ‏.‏