Is it mandatory to escape tabulator characters in C and C++?

In C and C++ (and several other languages) horizontal tabulators (ASCII code 9) in character and string constants are denoted in escaped form as '\t' and "\t". However, I am regularly typing the unescaped tabulator character in string literals as for example in "A B" (there is a TAB in betreen A and B), and at least clang++ does not seem to bother - the string seems to be equivalent to "A\tB". I like the unescaped version better since long indented multi-line strings are better readable in the source code.

Now I am asking myself whether this is generally legal in C and C++ or just supported by my compiler. How portable are unescaped tabulators in character and string constants?

Surprisingly I could not find an answer to this seemingly simple question, neither with Google nor on stackoverflow (I just found this vaguely related question).