How did Abdullah ibn al-Mubarak acquire knowledge?

Abdullah ibn al-Mubarak, whose kunya was Abu Abd al-Rahman al-Hanzali al-Marwazi, was born in the year 118 AH. He encompassed all good qualities: knowledge, jurisprudence, asceticism, courage, and generosity. Imams praised him, such as Ahmad ibn Hanbal, who said: "In the time of Ibn al-Mubarak, there was no one more eager for knowledge than him." Abd al-Rahman ibn Mahdi said: "I have never seen anyone more sincere towards the Ummah than Abdullah ibn al-Mubarak." Al-Dhahabi titled him "Shaykh al-Islam." He began seeking knowledge at the age of twenty, traveled extensively, and heard from prominent scholars. He frequently stayed in his home to read Hadith, saying: "How can I feel lonely when I am with the Prophet, peace and blessings be upon him, and his Companions?!" He was quick to memorize. He passed away in the year 181 AH, at the age of 63.