Midrash su Salmi 119:20

Raba said further: "One shall first study, and thereafter deliberate, as the above-cited verse reads, the law of the Lord, and thereafter, and in his law shall he meditate." Raba said further: "One shall study, even though he forgets it; one shall study, although he does not understand it well. (Ps. 1, 3) And he shall be like a tree replanted by streams of water. Said the disciples of Janai: "Replanted, and not planted; this signifies that he who receives his knowledge from one teacher, will never see any blessing [in his studies]." R. Chisda said to his disciples: "I would like to tell you something, but I am afraid you will leave me, and go away. He who studies always from one teacher, will never see any blessing." They then left him and went to the college of Raba, who, when he heard the above reason, said to them: "It is true only concerning reasons and ingenuity; but as for traditions, it is better to learn them from one master, (Ib. b) in order to avoid different versions." R. Tanchum b. Chanilai said: "It is advisable to divide one's years into three parts: one-third for the study of Scripture, the second, for Mishna, and the third, for Talmud." But does one know how long he is going to live? It refers to the days. The fruit in its season … does not wither. Said Raba: "This means, that if the fruit is given in its season, then its leaves will not wither; but if not, then upon both, the teacher and the scholar, will the succeeding verse be applied; not so the wicked, etc."