Musnad Ahmad 937:120

'Abd al-Rahman narrated to us, from Sufyan, from Wasil, from al-Ma'rur, from Abu Dharr, from the Prophet, peace and blessings of Allah be upon him, who said: "Your brothers are those whom Allah has placed under your hands. So, whoever has his brother under his hand, let him feed him from what he eats, and let him clothe him from what he wears. And do not burden him with what overcomes him (is too difficult for him). If you do burden him with what overcomes him, then help him with it."