Musnad Ahmad 788:102

Waki’ narrated to us, Sufyan and ‘Abd al-Rahman narrated to us, from Sufyan, from Hakim ibn Daylam, from Abu Burdah, from his father, who said: The Jews used to sneeze in the presence of the Prophet, may Allah bless him and grant him peace, hoping that he would say to them: "May Allah have mercy on you." So he would say to them: "May Allah guide you and rectify your affairs."