The most common and most likely answer to this crossword clue is the 9 letter word GOODNIGHT
I've seen this crossword clue in The Times
G
O
O
D
N
I
G
H
T
More clues leading to the result GOODNIGHT
- I’m turning in skilled horseman to get a hearing
- . Daughter close to tears initially after sentimental stuff in farewell
- Try doing the exercise when lacking energy – I’m off!
- Nearly occupies considerable time giving evening’s final speech?
- Expression used when turning in honourable noble that’s abandoned king
- Final message worthy warrior’s spoken
Buddy explains!

The straight part
We know that "I’m turning in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i’m turning in = goodnight.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GOODNIGHT mean?
GOODNIGHT noun- Alternative spelling of good night