תלמוד על איכה 3:27

When one person sits alone and engages in Torah, his reward is accrued on High, as it says (Lamentations 3:27), “Let him sit alone in silence, for God has placed it upon him.” They gave a parable: To what can this be compared? [It can be compared] to someone who had a young son whom he left alone and went out to the marketplace. The boy went and got a scroll and placed it on his knees, and was sitting and studying it when his father came back from the marketplace. The father said: Look at my young son whom I left alone when I went to the marketplace! What did he do? He took it upon himself to study, and he went and got a scroll and placed in on his knees and sat and studied it! You learn from this that even one person who sits alone and engages in study accrues his reward on High.