Musnad Ahmad 1118:5

Abu Abd al-Rahman al-Muqri narrated to us, Haywah narrated to us, he said: Abu Hani informed me, from Amr ibn Malik, that he narrated to him that he heard Fadalah ibn Ubayd saying: When the Messenger of Allah (peace and blessings of Allah be upon him) would pray with the people, men would fall from their standing position during the prayer due to the hunger they were suffering, and they were the People of the Suffah (Ahl al-Suffah), until the Bedouins would say: "These people are mad." When the Messenger of Allah (peace and blessings of Allah be upon him) would finish the prayer, he would turn to them and say: "If you knew what you have with Allah, you would love to have even more need and poverty." Fadalah said: And I was with the Messenger of Allah (peace and blessings of Allah be upon him) on that day.