Bukhari :: Book 3 :: Volume 31 :: Hadith 195
Narrated 'Abdullah bin 'Amr bin Al-'As:
"Once Allah's Apostle 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 replied, "Half of the year," (i.e. he used to fast on every alternate day).
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