Muhammad bin Bashr bin al-Farafsa محمد بن بشر بن الفرافصة العبدي · The Book of Fasting

: "The Messenger of Allah said: 'Fast when you see it and stop fasting when you see it, and if it is obscured from you (too cloudy), then count it as thirty (days).'"

"The Messenger of Allah said: "The Messenger of Allah said: Do not fast before Ramadan. Fast when you see it and stop fasting when you see it, and if clouds prevent you from seeing it, then complete Thirty (Days)."'

he asked the Messenger of Allah about fasting while traveling. He said: "If you wish to fast then fast, and if you wish not to fast then do not fast."