Being kind to one for whose faith there is concern because it is weak; Prohibition of attributing Faith to someone without definitive evidence

It is narrated on the authority of Sa'd that the Messenger of Allah (ﷺ) bestowed upon a group of persons (things), and Sa'd was sitting amongst them. Sa'd said: The Messenger of Allah (ﷺ) ignored some of them. And he who was ignored seemed to be more deserving in my eyes (as compared with others). I (Sa'd) said: Messenger of Allah I why is it that you did not give to such and such (man)? Verily I see him a believer. Upon this the Messenger of Allah (ﷺ) observed: Or a Muslim? I kept quiet for some time but I was again impelled (to express) what I knew about him. I said: Messenger of Allah why is it that you did not give it to such and such? Verily, by Allah, see him a believer. Upon this the Messenger of Allah (ﷺ) remarked: (Nay, not a believer) but a Muslim. He (Sa'd) said: I again kept quite for some time but what I knew about him again impelled me (to express my opinion) and I said: Why is it that you did not give (the share) to so and so: By Allah, verily I see him a believer. The Messenger of Allah (ﷺ) remarked; (Nay, not so) but a Muslim. Verily (at times) I give (a share) to a certain man apprehending that he may not be thrown prostrate in the Fire, whereas the other man (who is not given) is dearer to me (as compared with him).