You know that
Prophet Muhammad  is mentioned by name in the Song of Solomon chapter 5 verse 16: 

Translation ??

 Hikko Mamittakim we kullo Muhammadim Zehdoodeh wa Zehraee Bayna Jerusalem.
His mouth is most sweet: yea, he is altogether lovely. 
This is my beloved, and this is my friend, O daughters of Jerusalem.

In the Hebrew language -im is added for respect.

 Similarly -im is added after the name of Prophet Muhammad (pbuh) to make it Muhammadim. 

In English translation they have even 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.