From Ye Shaoweng's (
叶绍翁, Southern Song) 《
游园不值》:
春色满园关不住,
一枝红杏出墙来。 (The garden's spring cannot be shut in - one red apricot branch leans out over the wall.) The poet, denied entry to a garden, notices a single branch escaping over the wall - and decides that's enough to know spring is inside.