The first Shia Imam, Ali ibn Abitaleb Amiral Momeneen (AS) said:

If you think that I have doubts about fighting Shaamis (the army from Shaam), swear to God, each day that I delay the war is because I wish some of them join us and be guided; and in all the darkness, see my light and rush toward me, and that is better for me than killing them while they are being misguided. Although in this case they will also get in trouble for their sins [1].

[1] Nahjul Balaghah, Sermon 55.

Source: en.shafaqna.com