Imam Muslim's Early Hadith Learning:

At the age of eighteen, he began his study of Hadith by listening to Yahya ibn Yahya al-Tamimi — and at that time, both listening (sama‘) and writing were essential and inseparable. In 220 AH, he performed Hajj and in Makkah he heard and recorded hadith from ‘Abdullah ibn Maslamah al-Qa‘nabi, one of the foremost students of Imam Malik. In Kufa, he studied hadith from a group of scholars including Ahmad ibn Yunus, as documented in Siyar A‘lam al-Nubala’ (12/558) and Tadhkirat al-Huffaz (1/281). Later, he learned hadith from around 220 teachers in the regions of the Haramain, Iraq, and Egypt. The common method of hadith acquisition at the time involved hearing the hadith with full chains of narration (isnad) and recording them in writing.