ask-out Is (-) a must?

Question

When we write ask out (meaning ask for date) should we write hypen (-)? Is it a must

Answer 1

No, I don't think I've ever seen it with a hyphen. Normally when a verb-particle combination takes a hyphen, the resulting word is a noun: a fly-out, a shoot-out, a rip-off. So I suppose an instance of asking someone out could be called an ask-out (though as I say I haven't seen it), but the action would not.

Answer 2

"Ask out" is not what is called a semi-compound word, so no, a hyphen is not a must. Here's a link which may be of help to you:
http://owl.english.purdue.edu/handouts/grammar/g_hyphen.html