Musnad Abu Ya'la al-Mawsili 106:35

Ahmad ibn Ibrahim al-Mawsili narrated to us, Abu Ali Salih ibn Umar narrated to us, from Yazid ibn Abi Ziyad, from Abd al-Rahman ibn Abi Layla, from al-Bara ibn Azib, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever calls Medina 'Yathrib', let him seek forgiveness from Allah."