Musnad Ahmad 30:1716

Muhammad ibn Abdullah—meaning Abu Ahmad al-Zubayri—narrated to us, he said: Ubaydullah—meaning Ibn Abdullah ibn Mawhab—informed us, he said: My paternal uncle, Ubaydullah ibn Abd al-Rahman ibn Mawhab, informed me, from Abu Hurayrah, from the Messenger of Allah (peace and blessings of Allah be upon him), who said: "If one of you knew what he incurs by walking in front of his brother while he is conversing with his Lord, it would be more beloved to him to stand in that place for one hundred years than to take that step."