Musnad Ahmad 26:2

Hashim narrated to us, Husayn informed us, from Kathir ibn Mudrik al-Ashja‘i, from ‘Abd al-Rahman ibn Yazid, that ‘Abdullah [ibn Mas‘ud] recited the Talbiyah when he departed from Jam‘ [Muzdalifah]. It was said: "Is this a Bedouin?" He replied: "Has ‘Abdullah forgotten, or have the people gone astray? I heard the one upon whom Surah al-Baqarah was revealed saying in this place: 'Labbayk Allahumma Labbayk (Here I am, O Allah, here I am).'"