Is the statement ''I will smile when I kill'' from the Prophet ﷺ? - Q&A - Sh. Shady Alsuleiman

Some Muslims want to portray Muhammad ﷺ as thirsty for the blood of non-Muslims. They often attribute to him the statement ''I will smile when I kill'', but is this statement really from the Prophet of Islam, and is it true that he was sent to slaughter the non-Muslims?