The Madinan Period II, Part 9: The Truce Broken, Abū Sufyān in Madīnah, and the Letter of Ḥāṭib
Section 3 of 11 · The Life of the Prophet Muhammad: The Madinan Period, Part Two
"You Have Been Helped, ʿAmr ibn Sālim"
ʿAmr ibn Sālim al-Khuzāʿī, one of the men of Khuzāʿah, immediately went to Madīnah to convey the news of what had happened to the Messenger of Allah (peace be upon him). And he delivered the news to Muḥammad (peace be upon him) in lines of poetry, reminding Muḥammad (peace be upon him) of their alliance, and reminding him of the alliance they had had with his great-grandfather Hāshim. What was the response of the Messenger of Allah (peace be upon him)? If such a situation were brought to the leaders of today, they would probably say: let us take it to the United Nations, or let us see what the Security Council will say, or let us consult the international community — or other ways of getting out of their responsibility. When ʿAmr ibn Sālim presented this to the Messenger of Allah (peace be upon him), the Messenger of Allah (peace be upon him) gave him a clear, direct and decisive answer. He told him: nuṣirta yā ʿAmra bna Sālim. One word. The Messenger of Allah (peace be upon him) told him: you have been helped, ʿAmr ibn Sālim. That is it: you will get the help. He did not tell him how; he did not give him the details; he gave him this promise. Nuṣirta yā ʿAmra bna Sālim: you are helped; it is done; it is over. And then a cloud passed by, and the Messenger of Allah (peace be upon him) said: this cloud is giving me the glad tidings of support and help for Banū Kaʿb — and Banū Kaʿb are the people of Khuzāʿah.
Back to something mentioned earlier. See the statement of Ibn Isḥāq. He said: fa-kharaja Muʿāwiyatu bnu Nawfal al-Dīlī fī qawmihi, wa huwa yawmaʾidhin sayyiduhum wa qāʾiduhum, wa laysa kullu banī Bakrin tābaʿah — Muʿāwiyah ibn Nawfal al-Dīlī went out with his people, and he was their leader, but not all of Banū Bakr followed him. Even though not all of Banū Bakr followed Muʿāwiyah, the Messenger of Allah (peace be upon him) considered what happened sufficient for the covenant to be ended and for war to be announced against the people of Makkah. And he did not announce to the people of Makkah his intention of attacking them; in fact, it was done secretly; it was a clandestine operation. The Messenger of Allah (peace be upon him) made duʿāʾ to Allah: O Allah, conceal the news, and blind their eyes from seeing us or knowing of our advance. And that is what happened: the people of Quraysh only learned of the advance of the Muslim army when it was on the outskirts of Makkah.
Therefore, not all of the population needs to be supportive of what the government does for it to be considered a breach of the covenant between them and the Muslims. For example, if people come out in demonstrations against a war, or some of the government is against the war — as long as part of the government has taken the official stance of attacking the Muslims, the leader of the Muslims has the right to announce war and fight against that particular nation. So the Messenger of Allah (peace be upon him), immediately after that, started preparations.