no matter

You need the "whether". It is not optional.

Disgree again with Tes, WB. It's often said without the "whether"

Tes, tho smart as can be, gets involved with technicalities

Agree with TYN, but the sense is clear, in informal speech, if you leave it out (or replace it with "if". But "whether" is better because it's clearer imho.)

These foreign learners are not asking if some way of saying something would be OK to say to the good ol' boys who chew the fat down at the trucker's bar in East Jesus, Oklahoma, they are asking about what they think of as "proper English". It therefore behoves us to answer accordingly.

I disagree but guess I'm just a disagreeable person

WB, what's your opinion

Um...my opinion is, excellent answers. Thank you.

Quite welcome WB