Sefer HaBahir

Rabbi Amorai said, “Why is it written, ‘YHVH is a man of war’ (Exodus 15:3)?" Mar Rachumai said to him, "My teacher, you should not ask a simple word! Hear me, and I will advise you." He [Mar Rachumai] said to him, "To what may this be compared? To a king who had beautiful dwellings, who gave a name to every single one of them, and each one of them was better than the last. He said, 'I will give this dwelling that is named Aleph to my son. But the one named Yud is also good, and the one named Shin is also good!' What did he do? He gathered together all three, made one name from them, and made one house from them." He [Rabbi Amorai] said to him, "Until when will you conceal your words?!" He [Mar Rachumai] said to him, "My son, Aleph is first, Yud is second to her, Shin includes the whole world. Why does Shin include the whole world? Because teshuvah [repentance] is written with her."