The Messenger of Allah said: "The most virtuous fast is the fast of my brother Dawud. He would fast a day, and not fast (the next) day. He would not flee at the time of engagement (with the enemy)."
Jami` at-Tirmidhi Book 8, Hadith 89
← Previous Hadith Anas bin Malik was asked about the Prophet's fasting and he said: "He would fast during a month until we thought that he did not want to abstain from fasting during any of it. And, he would not fast during a month until we thought that he did not want to fast during any of it. (There was no time) that I wanted to see if he was performing Salat during the night, except that I would see him praying, nor to see him sleeping, except that I would see him sleeping."

Jami` at-Tirmidhi Book 8, Hadith 88 Next Hadith → "I witnessed Umar bin Al-Khattab on the Day of Nahr beginning with the Salat before the Khutbah. Then he said: 'I heard the Messenger of Allah prohibit fasting on these two days. As for the Day of Fitr, then it is for you to take a break from your fasting, and a celebration for the Muslims. As for the Day of Adha, then eat from the flesh that you have sacrificed.'"

Jami` at-Tirmidhi Book 8, Hadith 90