Musannaf Ibn Abi Shaybah 7971 — Those who lengthened the first two

Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) said: We used to estimate the length of the standing of the Prophet (peace and blessings be upon him) in Zuhr and Asr. In the first two rak'ahs of Zuhr he would recite about thirty verses, and in the last two rak'ahs he would stand for half of that. Likewise, in the first two rak'ahs of Asr he would stand as long as the last two rak'ahs of Zuhr, and in the last two rak'ahs of Asr he would stand for half as long as the first two.