We used to estimate how long the Messenger of Allah ﷺ would stand in the Zuhr and Asr prayers. We estimated his standing in the first two units of Zuhr to be about the length of reciting thirty verses, roughly the length of Surah as-Sajdah. We estimated his standing in the last two units to be about half of that. As for Asr, we estimated his standing in the first two units to be about half of that, and his standing in the last two units to be about half of the first two.
حدثنا هشيم حدثنا منصور يعني ابن زاذان عن الوليد بن مسلم عن أبي المتوكل أو عن أبي الصديق
كنا نحزر قيام رسول الله ﷺ في الظهر والعصر قال فحزرنا قيام رسول الله ﷺ في الظهر في الركعتين الأوليين قدر قراءة ثلاثين آية قدر قراءة سورة تنزيل السجدة قال وحزرنا قيامه في الأخريين على النصف من ذلك قال وحزرنا قيامه في العصر في الركعتين الأوليين على النصف من ذلك قال وحزرنا قيامه في الأخريين على النصف من الأوليين
Its isnad is sahih. Mansur is trustworthy and firmly reliable, and Abu Siddiq, Bakr bin Amr Naji, is trustworthy, and Walid bin Muslim is trustworthy except that he practices tadlis, and here he has used the ambiguous form "an", which would normally make his hadith daif. However, the hadith is connected and well known, and Walid has explicitly stated that he heard it directly in other versions. See Sahih Muslim 1/34, no. 452, in the Book of Prayer, chapter on reciting during Dhuhr and Asr, and Abu Dawud 1/213, no. 804, and Ibn Majah has also brought it through another route, 1/271, no. 828.His saying, "we used to estimate," means we would gauge and guess.