"I heard him saying" - meaning the Prophet (ﷺ) - "while supplicating against the Ahzab: 'O Allah, Revealer of Book! Severe is reckoning! Rout the Ahzab and shake them.'"

There is something on this topic from Ibn Masu'd

This Hadith is Hasan Sahih.

Jami` at-Tirmidhi Book 23, Hadith 9