How to include a text file into Mautic base template

My Mautic version is: 2.16.1
My PHP version is: 7.0.33-0+deb9u6

My Issue:
I have a simple file body.html with text content where I placed at
I want to include their content in betweeen of my Template.

So, on my page.html.twig I have addes the following:

{{ source('{{ getAssetUrl("body.html", null, null, true) }}', ignore_missing = true) }}

But it does not work. It only work if I make this:

{{ source('/home/mydomaincom/public_html/body.html', ignore_missing = true) }}

The problem is that it will not help me out.

Please can anyone tell me what can I do to make the expression bellow work?

{{ source('**PLEASE WHAT PUT HERE ?**', ignore_missing = true) }}

I have done all I could, have visited all the documentation I found regarding Twig and I could not fine why it happens.

Thanks in advanced.