Dear Robert,

Thank you for the relevant note. It's a luxury to feel free in
translation, knowing that occasional mistakes will be corrected.

There is a passage Itivuttaka-Atthakattha 1.85:

sammappa~n~naaya passatiiti sammaa hetunaa ~naayena
vipassanaapa~n~naasahitaaya maggapa~n~naaya
pari~n~naapahaanasacchikiriyaabhaavanaabhisamayavasena passati.

which clearly indicates instrumental case.

So:

"Rahula, whatever form, - past, future or present, internal or
external, gross or subtle, base or exalted, whether it is far or
near, - all form should be seen as it really is with right wisdom
in such a way: "This is not mine, I am not this, this is not
me".

Best wishes,
Dimitry