From the lesson on "Encouragement and Warning," discussing "Musnad of Imam Ahmad (may Allah have mercy on him)."

The Shaykh : ... the musnads, and specifically among them "Musnad of Imam Ahmad," which is the most extensive and abundant of the musnads that we have in our hands today, as I have mentioned. Among what the scholars mention, there is nothing more extensive except "Musnad of Baqi ibn Makhlad - or Makhlad -," and this, unfortunately, still remains in the realm of manuscripts. In "Musnad of Imam Ahmad" that we have in our hands today, the second part, its second volume, reaches for us six hundred pages. The second half of it is dedicated solely to the musnad of Abu Hurayrah, and the first half collects the musnads of 'Abdullah ibn 'Umar ibn al-Khattab, 'Abdullah ibn 'Amr ibn al-'As, and a third Companion known by his kunyah, which is Abu Rumthah. So the musnads of these three form the first half of the second volume of "Musnad of Imam Ahmad," and the entire second half is the musnad of Abu Hurayrah.