Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: When the Messenger of Allah (peace and blessings be upon him) left Makkah, Sayyiduna Abu Bakr (may Allah be pleased with him) said: "Inna lillahi wa inna ilayhi raji'un (We belong to Allah and to Him we return). The Messenger of Allah (peace and blessings be upon him) has been driven out; they will surely all be destroyed." Then when this verse was revealed: "Permission has been given to those who are being fought, because they were wronged, and indeed Allah is fully capable of giving them victory" [Surah al-Hajj: 39], "Those who were driven out of their homes unjustly" [Surah al-Hajj: 40], Sayyiduna Abu Bakr (may Allah be pleased with him) knew that there would now be fighting.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12284