Usama b. Zaid said

Allah's Messenger ﷺ sent us to some people of Juhaina, and I attacked one of them and was about to spear him when he said, “There is no Allah but Allah.” I then speared him and killed him, after which I went and told the Prophet. He said, “Did you kill him when he had testified that there is no Allah but Allah?” I replied, “ Messenger of Allah , he did that only as a means to escape death.” He asked, “Why did you not split his heart?”* (Bukhari and Muslim.) *He is here rebuked for attributing motives to the man when he could not know his inner motive. Splitting the heart is a figure of speech for examining the inner motives. In the version of Jundub b. ‘Abdallah al-Bajali Allah's Messenger ﷺ is reported as saying several times, “How will you deal with ‘There is no Allah but Allah’ when it comes on the day of resurrection?” Muslim transmitted it.