´Sa'd bin Malik said:` "The Messenger of Allah came to visit me while I was sick. He said: 'Do you have a will?' I said: 'Yes.' He said: 'For how much?' I said: 'All of my wealth, for the cause of Allah.' He said: 'What did you leave for your children?'" He (Sa'd) said: "They are rich in goodness.' He said: 'Will a tenth.'" He (Sa'd) said: "He (pbuh) continued decreasing it until he said: 'Will a third, and a third is too great.'" (One of the narrators:) Abdur-Rahman said: "We considered it recommended that it be less than a third, since the Messenger of Allah said: 'And a third is too great.'"
Hadith Referenceسنن ترمذي / كتاب الجنائز عن رسول الله صلى الله عليه وسلم / 975