You were a darling to help, I could never have done it without you.
5 seconds sound clip from the Breakfast at Tiffany's movie soundboard.
You can hear this line at 00:12:24 in the Blu-ray version of the movie.
Quote context
[...]
- But then he told me his client was Sally Tomato.
- He said dear old Sally had seen me at Elmo's or somewhere, and had admired me à la distance.
- So wouldn't it be a good deed if I were to visit him once a week?
- Well, how could I say no? It was all so wildly romantic.
- Very good. I must say I'm amazed.
- You were a darling to help, I could never have done it without you.
- Bag.
- Call me anytime. I'm just upstairs, or I will be as soon as I get moved in.
- You mean he gives you $100 for an hour's conversation?
- Well, Mr O'Shaughnessy does as soon as I meet him, and give him the weather report.
[...]