Hisham bin Abi 'Abdullah al-Dastawa'i هشام بن أبي عبد الله الدستوائي · The Book on Fasting

Zaid bin Thabit said: "We ate Sahar with the Messenger of Allah, then we stood for the Salat." I (Anas) said: "How long was that?" He said: "About the lengthy of fifty Ayahs."