觀無量壽佛經疏 3.182

3.182

九、從眾生但觀首相已下，正明勸觀二別。云何二別？觀音頭首上有一立化佛，勢至頭首之上有一寶瓶。

Ninth, from “sentient beings need only contemplate the head” onward, it directly explains exhorting contemplation of the two distinctions. What are the two distinctions? On the head of Avalokiteśvara there is a standing transformation Buddha; on the head of Mahāsthāmaprāpta there is a jeweled vase.