مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3526
Musnad of Abdullah bin Mas'ood
It was narrated from "Abdur-Rahman bin Yazeed that 'Abdullah recited the Talbiyah when he moved on from Muzdalifah, and it was said: is this man a Bedouin? 'Abdullah said: Have people forgotten or gone astray? I heard the one to whom Sooratal-Baqarah was revealed saying in this place: “Labbaik Allahumma labbaik.”
Musnad Ahmad 3549Its isnad is saheeh, Muslim (1283)]