Musannaf Ibn Abi Shayba 28:891

Abdullah ibn al-Mubarak narrated to us, from Ibn Jurayj, from Ata’, who said: Silence and remembrance became obligatory at the time of trembling (shaking/fear). He said: Then he recited: "So stand firm and remember Allah much." He said: I said, "And should one recite the remembrance aloud?" He said: He said, "Yes."