From Sahih Bukhari (Hadith 1974):
Narrated `Abdullah bin `Amr bin Al-`As:"Once Allah's Messenger (ﷺ) came to me," and then he narrated the whole narration, i.e. your guest has a right on you, and your wife has a right on you. I then asked about the fasting of David. The Prophet (ﷺ) replied, "Half of the year," (i.e. he used to fast on every alternate day)
Reference: Bukhari 1974