Hadith 2

And from him, from his father, from Muhammad Bin Yahya Al Attar, from Muhammad bin Ahmad Bin Yahya, from Ibrahim Bin Is’haq, from Muhammad Bin Al-Hassan Bin Shamoun, from Abu Hashim who said, ‘I said to Abu Al-Hassan Al-Maazy (7th Imam-asws), ‘Why have the Obligatory Salat and the Sunnah Made to be of fifty Cycles, neither increasing in it nor reducing from it? ’
He-asws said: ‘The hours of the night are twelve hours, and in what is between emergence of the dawn to the rising of the sun, there is an hour. And the hours of the night are twelve hours. So each two Cycles have been Made to be for every hour, and what is between the setting of the sun up to the fall of the twilight is ‘Gasaq’ (darkness)’’. [2]