Ibn Hibban

Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates: We used to estimate the standing (qiyam) of the Prophet (peace and blessings of Allah be upon him) in the Zuhr and Asr prayers. So we estimated that in the first two rak'ahs of the Zuhr prayer, his standing was as long as the recitation of thirty verses, and regarding his standing in the last two rak'ahs, we estimated that it was half of that. And in the first two rak'ahs of the Asr prayer, we estimated that his standing was as long as the last two rak'ahs of Zuhr, and regarding the last two rak'ahs of Asr, we estimated that it was half of that. (Imam Ibn Hibban, may Allah have mercy on him, says:) The statement of Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) that we estimated the standing in the first two rak'ahs to be as long as the recitation of thirty verses, apparently seems contrary to the statement of Sayyiduna Abu Qatadah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) used to make the first rak'ah long and the second rak'ah short. However, praise be to Allah, it is not so. Because in the first rak'ah, the Prophet (peace and blessings of Allah be upon him) would recite thirty verses with pauses, in a measured and melodious tone, and in the second rak'ah, he would recite the same number of verses without pauses and melody. So the recitation would be equal in both, but the first rak'ah would be longer than the second.