Musannaf Ibn Abi Shayba 28:776

'Abd al-Rahim ibn Sulayman narrated to us, from 'Abd al-Malik, from 'Ata', who said: The fifth [share] of Allah and the fifth [share] of the Messenger is one. The Prophet (peace and blessings of Allah be upon him) used to place that fifth wherever he liked, and he would do with it what he willed, and he would support with it whomsoever he willed.