From Sahih Muslim (Hadith 1015):
Abu Sa'id al-Khudri reported:The Apostle of Allah (ﷺ) used to recite in every rak'ah of the first two rak'ahs of the noon prayer about thirty verses and in the last two about fifteen verses or half (of the first rak'ah) and in every rak'ah of the 'Asr prayer of the first two rak'ahs about fifteen verses and in the last two verses half (of the first ones)
Reference: Muslim 1015