A friend in need - Idioms by The Free Dictionary
a friend in need
friend in need
A person who is dependable and a good friend in difficult times. Taken from the proverb "a friend in need is a friend indeed." Michelle stayed with me in the hospital when I broke my ankle. A friend in need is a friend indeed.
a ˌfriend in ˈneed (is a ˌfriend inˈdeed) (saying) a friend who helps you when you are in trouble (is a real friend): I’ll always be grateful to Tom for helping me; a friend in need is a friend indeed!
References in classic literature
Think twice before you speak to a friend in need
This really notable man was a friend in need
to the telephone.