assalaamu alykum wah rahmatullahi wah barakatuhu
amazing talk about amazing special people, playlist is on the first vid Alhamdulillah
Allah knows best but ustadh bilal Assad makes mention of this on the timestamp @39.37,
saying imam ahmad bin hanbal would do 300 rakats daily and then when he became 77 years of age due to bad health he reduced it down to 150 rakats, subhanAllah