It was narrated from ‘Ubadah bin Samit that the Prophet ﷺ awarded one quarter of the spoils to those who attacked the enemy at the beginning and one third to those who attacked at the end. (Using translation from Ibn Mājah 2852)
أَنَّ رَسُولَ اللهِ ﷺ «نَفَلَ فِي الْبَدْأَةِ الرُّبُعَ وَفِي الرَّجْعَةِ الثُّلُثَ»