Prophet Muhammad (pbuh) is mentioned by name in the Song of Solomon chapter 5 verse 16:
In the Hebrew language 'im' is added after certain words for respect. Similarely 'im' is added after the name of Prophet Muhammad (pbuh) to make it 'Muhammadim'. In the English translation they have translated the name of Prophet Muhammad (pbuh) as "altogether lovely", but in the Old Testament in Hebrew, the name of Prophet Muhammad (pbuh) is yet present.