WIST

Believe me, it is not length of time spent in prayer that brings a soul benefit: when we spend our time in good works, it is a great help to us and a better and quicker preparation for the enkindling of our love than many hours of meditation.

Teresa of Ávila (1515-1582) Spanish mystic, poet, philosopher, saint
Foundations, ch. 5 “On Prayer” [tr. Peers]
    (Source)

Alternative translations:

And let souls believe me that it is not the length of time spent in prayer that benefits one; when the time is spent as well in good works, it is a help in preparing the soul for the enkindling of love. The soul may thereby be better prepared in a very short time than through many hours of reflection.
[tr. Kavanaugh / Rodriguez]

And, believe me, it is not the length of time which makes a soul advance in prayer, but when being called to other works by obedience and charity, they do these duties well, then (as I have said) the soul advances so much, that in a very short time she is better prepared for enkindling within her the love of God, than (wanting in those works) she would be by spending many hours in meditation.
[tr. Dalton]

But believe me, what helps a soul to advance is not the spending long hours in prayer, but it is a great help to be employed also in active works, so that the soul is better disposed to enkindle its love in a very short space of time than by spending many hours in meditation.
[tr. Mason]