Musar על אבות 1:15

And if you should say, "After I gather some money, and after I am free of my business affairs, then I will return and read and study the Torah" — if such a thought should come into your heart, then you will never acquire the crown of the Torah. But "fix a period for the study of Torah" (Aboth 1:15), and let your daily work be secondary. "And do not say, 'When I have leisure I will study' for perhaps you will have no leisure' " (Aboth 2:5).