It was narrated that Imam Ali AS said:

أَ لَا تَرَوْنَ إِلَى أَطْرَافِكُمْ قَدِ انْتَقَصَتْ، وَإِلَى أَمْصَارِكُمْ قَدِ افْتُتِحَتْ، وَإِلَى مَمَالِكِكُمْ تُزْوَى، وَإِلَى بِلَادِكُمْ تُغْزَى! انْفِرُوا ـ رَحِمَكُمُ اللهُ ـ إِلَى قِتَالِ عَدُوِّكُمْ، وَلَا تَثَّاقلُوا إِلَى الْأَرْضِ فَتُقِرُّوا بِالْخَسْفِ، وَتَبُوءُوا بِالذُّلِّ، وَيَكُونَ نَصِيبُكُمُ الْأَخَسَّ، وَإِنَّ أَخَا الْحَرْبِ الْأَرِقُ، وَمَنْ نَامَ لَمْ يُنَمْ عنْهُ، وَالسَّلَامُ.

Do you not see that the boundaries of your cities have diminished, your populated areas have been conquered, your possessions have been snatched away and your cities and lands have been attacked. May Allāh have mercy on you, get up to fight your enemy and do not remain confined to the earth, otherwise you will face oppression and suffer ignominy and your fate will be the worst. The warrior should be wakeful because if he sleeps the enemy does not sleep; and that is an end to the matter.

Nahj al-Balāgha, To Egyptians through Malik al-Ashtar, upon his appointment as their governor, Hadith #380