Sunan an-Nasa'i 5752
سنن النسائي#5752SahihUbaidullah bin Sa'eed said:"I heard Abu Usamah say: 'I never saw any man more assiduous in seeking knowledge than 'Abdullah bin Al-Mubarak, not in Ash-Sham, Egypt, Yemen or the Hijaz
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih Isnaad Maqtu
Al-AlbaniSahih Isnaad Maqtu
Zubair Ali ZaiIsnaad Sahih
In-book reference: 51:214