Hadith 51:214
Sahih (Darussalam)
'Ubaidullah 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.'"
أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، قَالَ سَمِعْتُ أَبَا أُسَامَةَ، يَقُولُ مَا رَأَيْتُ رَجُلاً أَطْلَبَ لِلْعِلْمِ مِنْ عَبْدِ اللَّهِ بْنِ الْمُبَارَكِ الشَّامَاتِ وَمِصْرَ وَالْيَمَنَ وَالْحِجَازَ
Original Reference: Sunan an-Nasa'i 5752