待我长发及腰时我一定娶你
[dài wŏ zhăng fā jí yāo shí wŏ yī dìng qŭ nĭ]
'When I grow my hair to my waist, I will marry you.' It conveys the meaning that the person is determined and serious to fulfill a promise made earlier - most possibly about proposing when the right conditions are achieved, like letting their hair reach shoulder length.