[{So perhaps you would kill yourself}] that is, destroying yourself {on their tracks}, meaning: after they have left, {if they do not believe in this discourse}, meaning: the Quran, {out of grief}, that is: sadness for them.

Muhammad said: "Asafan" (out of grief) is in the accusative case as a verbal noun (masdar) acting in the position of a circumstantial qualifier (hal).