You can find several PRT file types that contain 3D parts or components, so there may be several different prt to sab conversions possible. SAB format is from ACIS and also somewhat well supported format, so you should have no trouble finding a program capable of prt to sab conversion.
Convert CAD 3D part or component to 3D ACIS binary file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert prt to sab on Windows
A dedicated CAD converter
Convert from prt file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.