Abū Isḥāq [Al-Fazārī] states:

The enemy was never able to stand up to the Companions of Allāh’s Messenger – Allāh’s praise and peace be upon him, so when the news of the defeat of the Romans came to Heraclius at Antioch he asked [his people], “Woe to you, tell me about these people who fight you, are they not humans like you?” They replied, “Indeed, they are.” He asked, “So are you more in number or them?” They replied, “We outnumber them greatly in all places.” He said, “So how is it that you are defeated whenever you meet them [in battle].” A senior and esteemed elder amongst them replied, “Because they stand in prayer at night, fast during the day, fulfill their agreements and promises, enjoin what is right and forbid what is evil, they are fair and just amongst themselves; and because we drink wine, fornicate, commit sin, break our agreements, steal, oppress and do injustice, enjoin the committing of what angers Allāh and forbid what pleases Allāh the Mighty and Majestic, and we cause evil and corruption in the land.” Heraclius said, “You are the one who has told me the truth.”

Abū Bakr Al-Daynūrī, Al-Mujālasah wa Jawāhir Al-‘Ilm 4:91.