Sahih al-Bukhari 27
Belief
If one does not embrace Islam truly but does so by compulsion or for fear of being killed (then that man is not a believer)
Narrated Sa'd: Allah's Messenger (ﷺ) distributed (Zakat) amongst (a group of) people while I was sitting there but Allah's Messenger (ﷺ) left a man whom I thought the best of the lot. I asked, "O Allah's Messenger (ﷺ) ! Why have you left that person? By Allah I regard him as a faithful believer." The Prophet (ﷺ) 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 Messenger (ﷺ) , "Why have you left so and so? By Allah! He is a faithful believer." The Prophet (ﷺ) again said, "Or merely a Muslim." And I could not help repeating my question because of what I knew about him. Then the Prophet (ﷺ) 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."