大乘起信論義記 3.517

3.517

如修多羅說，若人專念西方極樂世界阿彌陀佛，所修善根，迴向願求生彼世界，即得往生，常見佛故，終無有退。若觀彼佛真如法身，常勤修習畢竟得生，住正定故。

As a sūtra says: if a person single-mindedly is mindful of the Buddha Amitābha in the western realm of Ultimate Bliss, and with the roots of goodness cultivated dedicates them with the vow to seek rebirth in that realm, they will straightaway attain rebirth; because of constantly seeing the Buddha, they will ultimately never regress. If one contemplates that Buddha's tathatā dharmakāya and constantly and diligently cultivates, one will definitively attain rebirth, because one will abide in the correctly determined [rank].