Restricted-source polyglot string
brainfuck, 28 26 bytes

a+b[c-/[/---&lt;]&gt;&gt;- ]&lt;-.+.+.


Try it online!

Got the bf code from here.

Fails in Ink due to Expected target for new thread but saw '.+.+.'.

ink

abc//-&lt;&gt;-]-++


Try it online!

Ink will just print abc and the rest is a comment.

Fails in brainfuck due to mismatched bracket.