Musnad Ahmad 482:116

Abu Abd al-Rahman narrated to us, Haywah narrated to us, Bakr ibn Amr informed me, that Shu'ayb ibn Zur'ah informed him, he said: Uqbah ibn Amir al-Juhani narrated to me that he heard the Messenger of Allah, peace and blessings of Allah be upon him, saying to his companions: "Do not frighten your souls"—or he said: "the souls." It was said to him: "O Messenger of Allah, and what is frightening our souls?" He said: "Debt."