大方廣佛華嚴經隨疏演義鈔 18.8

18.8

疏「無心成行」等者，陶隱居云：「雲無心而出岫，鳥倦飛以知還。」凡舉雲義雖有多種，多明無心。

Regarding the Commentary's "Unintentional accomplishment of practice" and so forth: Tao the Recluse [Tao Hongjing] said, "Clouds without intent drift out from peaks; / Birds, weary of flying, know to return." Although various meanings are cited for clouds, they mostly clarify being without intent.