Harun bin Ishaq bin Muhammad هارون بن إسحاق بن محمد بن مالك · The Book on Fasting

The Messenger of Allah said: "When the night advances and the day retreats, and the sun is hidden, then the fast is to be broken."

Hamzah bin Amr Al-Aslami asked the Messenger of Allah about fasting while traveling, and he fasted regularly. So the Messenger of Allah said: 'If you wish then fast, and if you wish then break (the fast).'"

"Ashura was a day that the Quraish used to fast during Jahiliyyah, and the Messenger of Allah used to fast it. But when (the fast of) Ramadan became obligatory, the Ramadan was the required and Ashura was left. So whoever wanted to, he fasted it, and whoever wanted to, he left it."

"The Messenger of Allah would Yujawir (stay in I'tikaf) during the last ten (nights) of Ramadan and he said: 'Seek the Night of Al-Qadr during the last ten (nights) of Ramadan.'"