كتاب الصيام
13  
The Book of Fasting
(9)
Chapter: The virtue of sahur, which is recommended. It is recommended to delay it and to hasten the breaking of the fast
(9)
باب فَضْلِ السُّحُورِ وَتَأْكِيدِ اسْتِحْبَابِهِ وَاسْتِحْبَابِ تَأْخِيرِهِ وَتَعْجِيلِ الْفِطْرِ ‏‏
Sahih Muslim 1097 a

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.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعٌ، عَنْ هِشَامٍ، عَنْ قَتَادَةَ، عَنْ أَنَسٍ، عَنْ زَيْدِ بْنِ ثَابِتٍ، - رضى الله عنه - قَالَ تَسَحَّرْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم ثُمَّ قُمْنَا إِلَى الصَّلاَةِ ‏.‏ قُلْتُ كَمْ كَانَ قَدْرُ مَا بَيْنَهُمَا قَالَ خَمْسِينَ آيَةً ‏.‏
Reference : Sahih Muslim 1097a
In-book reference : Book 13, Hadith 58
USC-MSA web (English) reference : Book 6, Hadith 2415
  (deprecated numbering scheme)