觀彌勒上生兜率天經贊 2.185

2.185

The commentary says: Third is instructing in making the vow. If one has practice but no vow, that practice is inevitably isolated, and one will not necessarily attain rebirth in Maitreya's presence. If one has a vow but no practice, that vow is inevitably hollow, because when there was previously no cause, the fruit does not arise; therefore [the sūtra] instructs in making a vow to assist practice.