bash: __git_ps1: command not found error in virtual environment

Question

I created a virtual environment using pipenv. I activated it and opened it by using pipenv shell at the project directory. All my commands work properly. However, at the end it get the following error bash: __git_ps1: command not found.

What does this mean? How do I fix this?

The command line works perfectly and does not show this error when I use it outside the virtual environment.

I am using a MAC by the way.