It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that he (peace and blessings be upon him) used to recite in each of the first two rak'ahs of Zuhr about the measure of thirty verses, and in the last two rak'ahs of Zuhr the measure of fifteen verses, or half of that; and in each of the first two rak'ahs of Asr the measure of fifteen verses, and in the last two rak'ahs half of that.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2478