Sahih Bukhari Volume 001, Book 002, Hadith Number 026.
Sahih Bukhari Book 02. Belief
Narated By Sa'd : Allah's Apostle distributed (Zakat) amongst (a
group of) people while I was sitting there but Allah's Apostle
left a man whom I thought the best of the lot. I asked, "O
Allah's Apostle! Why have you left that person? By Allah I
regard him as a faithful believer." The Prophet commented: "Or
merely a Muslim." I remained quiet for a while, but could not
help repeating my question because of what I knew about him.
And then asked Allah's Apostle, "Why have you left so and so?
By Allah! He is a faithful believer." The Prophet again said, "Or
merely a Muslim." And I could not help repeating my question
because of what I knew about him. Then the Prophet said, "O
Sa'd! I give to a person while another is dearer to me, for fear
that he might be thrown on his face in the Fire by Allah."