Be firm when it's needed
Allah says, "Muhammad is the messenger of Allah, and those with him are firm against the disbelievers." (Al-Fath: 29)
"O Prophet, fight against the disbelievers and hypocrites, and be harsh with them. Their place is Hell — the worst return." (At-Taubah: 72)
"O believers, fight the disbelievers around you, and let them find you strong. Know that Allah is with those who are mindful of Him." (At-Taubah: 123)
(from Syajaratul Ma‘arif, Syaikh al-‘Izz bin Abdus Salam)