瑜伽師地論略纂 2.22

2.22

作意四力：初時三種，如其次第，緣未來、過去、現在境界；第四一力，通緣三世。　「若異此者，應於一所緣境，唯一作意，一切時生」者，若異前說四力生作意者，應於一境一作意恒生。由此故知，必由四力。

The four powers of attentiveness: The first three kinds take future, past, and present objects as their spheres, in respective order; the fourth single power takes the three times universally as its sphere. "If it were other than this, attentiveness would arise exclusively toward a single intentional object at all times": If it were different from the previously explained arising of attentiveness through the four powers, one attentiveness would constantly arise toward a single object. Therefore, we know it must depend upon the four powers.