Musnad Abu Ya'la al-Mawsili 6:36

Abu Khaythama narrated to us, Yahya narrated to us, from Ibn ‘Ajlan, he said: ‘Abdullah ibn Abi Salamah narrated to me that Sa‘d ibn Malik heard a man saying, “Labbayka Dha al-Ma‘arij” (At Your service, O Possessor of the Ways of Ascent). He said: “Indeed, Allah is the Possessor of the Ways of Ascent, but we did not use to say that with our Prophet, may Allah bless him and grant him peace.”