Talmud Bavli Avodah Zarah on Selection of Texts for Study

"Levi and Rabbi Shimon, the son of Rabbi Yehuda the Prince, were sitting before Rabbi Yehudah studying Scripture. Upon completing one book, Levi said, 'Let us now commence with the study of Proverbs,' while Rabbi Shimon said, 'Let us now commence with the study of Psalms'. Rabbi Shimon overruled Levi and they began to study Psalms. They paused after they had only reached the second verse, 'But his desire is in the Torah of the Lord'. Rabbi Yehudah explained: 'One should always study the section of Torah towards which his heart is inclined and wherein lies his desire'. Thereupon, Levi remarked: 'Rabbi, with this statement you have given me permission to rise up and withdraw myself from this study of the Psalms'."

-- Talmud Bavli, Avodah Zarah 19a