金光明最勝王經疏 1.147

1.147

贊曰：以三練磨策勤無退，名堅固精進。其心無礙如虛空。四弘不捨，名不斷大願。不退常修對。如空，通二。

Commentary: Urging oneself to exert diligence without retrogression through the three temperings is called 'Steadfast Exertion'. The mind is unobstructed like empty space. Not abandoning the four vast vows is called 'Unbroken Great Vows'. [This is] a pairing of non-retrogression and constant cultivation. Being like empty space connects to both.