It is narrated from Sayyiduna Habib bin Maslamah (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) set out on a military expedition, he would give a quarter as nafl after the khums, and when he returned, he would give a third as nafl after the khums.
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3512