Be a good Samaritan.

　　Help a lame dog over a stile.

　　eg：Be a good Samaritan and contribute much to the fund.

　　中英俚语俗语来源：水浒记传奇：“宋公明他扶危济困隐功曹。”

　　同义词：见义勇为 Do a good turn.

　　反义词：落井下石 When a dog is drowing, everyone offers him a drink.