From Li Bai's (
李白) Tang-dynasty poem 《
独坐敬亭山》 (Sitting Alone on Mount Jingting). Full couplet:
相看两不厌,只有敬亭山 - 'the one thing I never tire of looking at, and that never tires of me, is Mount Jingting.' After all his birds have flown and clouds have drifted off, only the mountain keeps him company.