When Omar consulted him about taking part in the Battle of Persia
Nahj al-Balāgha|Volume 1|Book 1|Chapter 146
إِنَّ هذَا الاْمْرَ لَمْ يَكُنْ نَصْرُهُ وَلاَ خِذْلاَنُهُ بِكَثْرَة وَلاَ بِقِلَّة، وَهُوَ دِينُ اللهِ الَّذِي أَظْهَرَهُ، وَجُنْدُهُ الَّذِي أَعَدَّهُ وَأَمَدَّهُ، حَتَّى بَلَغَ مَا بَلَغَ، وَطَلَعَ حَيْثُ طَلَعَ، وَنَحْنُ عَلَى مَوْعُود مِنَ اللهِ، وَاللهُ مُنْجِزٌ وَعْدَهُ، وَنَاصِرٌ جُنْدَهُ.
In this matter, victory or defeat is not dependent on the smallness or greatness of forces. It is Allāh’s religion which He has raised above all faiths, and His army which He has mobilised and extended, till it has reached the point where it stands now, and has arrived its present positions. We hold a promise from Allāh, and He will fulfil His promise and support His army.