Narrative:

Departed ZZZ. On climb out through FL200; first officer noticed odor. Seconds later; flight attendant called and reported odor in the cabin. First officer and captain donned O2 masks; [advised ATC]; and returned to ZZZ. Cause [was] APU oil leak.

Google
 

Original NASA ASRS Text

Title: A-321 Captain reported executing an air return due to odor during initial climb. Captain suspected odor caused by APU oil leak.

Narrative: Departed ZZZ. On climb out through FL200; First Officer noticed odor. Seconds later; Flight Attendant called and reported odor in the cabin. First Officer and Captain donned O2 masks; [advised ATC]; and returned to ZZZ. Cause [was] APU oil leak.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.