Quran 3:167 — The Amramites (Ali-'Imran)

And to expose the hypocrites who were told, "Come fight in the cause of GOD, or contribute." They said, "If we knew how to fight, we would have joined you." They were closer to disbelief then than they were to belief. They uttered with their mouths what was not in their hearts. GOD knows what they conceal.

[3:166] What afflicted you the day the two armies clashed was in accordance with GOD's will, and to distinguish the believers.

[3:168] They said of their kinsmen, as they stayed behind, "Had they obeyed us, they would not have been killed." Say, "Then prevent your own death, if you are truthful."