Visuddhimagga XVI-81

 Athassa yo tassā sammāvācākammantājīvasaṅkhātāya sīlabhūmiyaṃ patiṭṭhitassa tadanurūpo taṃsampayuttova kosajjasamucchedako vīriyārambho, esa sammāvāyāmo nāma. So paggahalakkhaṇo, anuppannaakusalānuppādanādiraso, micchāvāyāmappahānapaccupaṭṭhāno. 

（六）那住立于称为正语、正业、正命的戒地（的瑜伽）者的──随顺于彼（正语正业正命），与彼相应，正断懈怠的勤精进为「正精进」；策励是它的特相，未起的不善而令不起是它的作用，舍断邪精进是它的现状。

Ñ(XVI,81): When he is established on that plane of virtue called right speech, right action, and right livelihood, his energy, which is in conformity and associated with that [right view], cuts off idleness, and that is called right effort. It has the characteristic of exerting. Its function is the non-arousing of unprofitable things, and so on. It is manifested as the abandoning of wrong effort.