Sunan an-Nasa'i #3631 · The Book of Wills

"The Messenger of Allah visited me when I was sick, and said: 'Have you made a will?' I said: 'Yes.' He said: 'How much?' I said: 'For all my wealth to be given in the cause of Allah.' He said: 'What have you left for your children?' I said: 'They are rich (independent of means).' He said: 'Bequeath one-tenth.' And we kept discussing it until he said: 'Bequeath one-third, and one-third is much or large