Sahih al-Bukhari 1478

It is related that Sa'd said, "The Messenger of Allah, may Allah bless him and grant him peace, was distributing things to a group of people while I was sitting among them." He said, "The Messenger of Allah, may Allah bless him and grant him peace, left out a man whom I admired and did not give to him. I went to the Messenger of Allah, may Allah bless him and grant him peace, and spoke privately to him, 'Messenger of Allah, what about that person? By Allah, I see him to be a believer (mu'min).' He said, 'Or just a Muslim?' I was silent for a while and then what I knew about him became too much for me and I said,. 'Messenger of Allah, What about that person? By Allah, I see him to be a believer." He said, "I was silent for a while and then what I knew about him became too much for me and I said, 'What about that person? By Allah, I see him to be a believer.' He said, 'Or just a Muslim?' He said, 'I give to one man [and leave out] another I love more than him out of fear that Allah might throw him on his face into the Fire.'" It is related from Isma'il ibn Muhammad that he heard his father relate this. In his hadith, he said, "The Messenger of Allah, may Allah bless him and grant him peace, struck his hand, grasped me between the shoulder and neck and said, 'Advance, Sa'd, I will give to the man.'" Abu 'Abdullah said, "Kabukbu (17:94) is to fall headfirst. As for mukibb (grovelling) (67:22), a man grovels "akabba" when his action does not affect anyone else. When the action occurred, you say, 'Allah threw him on his face (kabba)' and you say 'I threw him (kababtuhu).'