Сефер ха-Бахир (Книга Сияния) 58

1[Rabbi Berachiah continued,] "Another interpretation: It teaches that souls fly out from there, as it is said, 'and [He] souled [וינפש]' (Exodus 31:17) until the thousandth generation, as is said, 'A word commanded to the thousandth generation' (Psalms 105:8). And next to it, 'That was cut with Abraham' (Psalms 105:9). What is 'that was cut'? [God] cut him a covenant between the ten fingers of his hand and then toes of his foot. Abraham was shamed. The Blessed Holy One said to him, 'Here, I have covenanted with you' (Genesis 17:4) and with it, you will be 'The father of a great nation' (Genesis 17:4)"