When he exhorted people to jihad but was met with silence
Nahj al-Balāgha|Volume 1|Book 1|Chapter 119
طَعّانينَ عَيّابينَ حَيّادينَ رَوّاغينَ.! انَّهُ لاَ غَنَاءَ فِي كَثْرَةِ عَدَدِكُمْ مَعَ قِلَّةِ اجْتَماعِ قُلُوبِكُمْ. لَقَدْ حَمَلْتُكُمْ عَلَى الطَّرِيقِ الْوَاضِحِ الَّتي لاَ يَهْلِكُ عَلَيْهَا إِلاَّ هَالِكٌ، مَنِ اسْتَقَامَ فَإِلَى الْجَنَّةِ، وَمَنْ زَلَّ فَإِلَى النَّارِ!
There is no benefit in the majority of your numbers because of lack of unity of your hearts. I have put you on the clear path whereon no one will perish except who perishes by himself. He who sticks to it would achieve Paradise and he who deviates goes to Hell.