It is narrated from Sayyiduna Habib bin Maslamah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) gave a quarter as nafl from what the people brought at the time of setting out, and on returning, a third after the khums.
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3511