a clear one. Indeed, its chain of transmission is not authentic either. Rather, it is most likely good. And Allah knows best.

2459 — “Whenever the Messenger of Allah, peace and blessings be upon him, prayed, he would whisper something that I could not understand, and he would not tell us about it. He said, ‘Did you notice me?’ We said, ‘Yes.’ He said, ‘I recalled one of the prophets who was given troops from among his people’—in another narration: ‘He was impressed by his community’—‘and said: Who can match these? Or who can stand up to them?’ Or he said something similar—in the other narration: ‘Who can stand up to them?’ without uncertainty. So it was revealed to him: Choose one of three things for your people: either We will set an enemy from outside them against them, or hunger, or death. He consulted his people concerning this, and they said: You are the Prophet of Allah, so the matter is entirely yours; choose for us. He then rose to pray—for whenever they were alarmed, they would turn to prayer—and prayed for as long as Allah willed. Then he said: O my Lord, not an enemy from outside them; nor hunger; rather, death. So death was unleashed upon them, and seventy thousand of them died [in one day]. Thus, what you see me whispering is: O Allah, by Your help I maneuver, for Your cause I charge, and by Your help I fight.’”

Aḥmad transmitted it (6/16): ʿAbd al-Raḥmān ibn Mahdī narrated to us; Sulaymān ibn al-Mughīrah narrated to us, from Thābit, from ʿAbd al-Raḥmān ibn Abī Laylā, from Ṣuhayb, who said … and then mentioned it. I say: This is an authentic chain of transmission according to the criteria of al-Bukhārī and Muslim. Maʿmar corroborated him, narrating from Thābit al-Bunānī through the same chain with something similar, but without the supplication at its end; and the other version—