Dear All:

In a Taiwanese-BBS board discussing English, one guy asked a question about how to use "whether or not" and "whether ... or not."
Another guy popped out a reply saying that the "or not" is wrong.
I gave him some links of the entry "whether" in some online dictionaries.

whether definition in Longman online dictionary
whether definition in Oxford learner's online dictionary
whether definition in Cambridge leaner's online dictionary

After half a day, he said that writing "or not" with "whether" is an awful expression, that is not allowed in formal English writing, and that the usages which dictionaries record are not suitable in formal writing.

What is/are your verdict(s)?

Best Regards
So what did he say was the alternative correct and formal way to write the sentences?
I'd say that everyone is entitled to his (or her) opinion and if he finds it objectionable, he should not use it, but he has no rational basis for this opinion and I dearly hope he is not an English teacher passing on such nonsense to students.