Midrasch zu Bereschit 31:53

This heap is witness between me and thee (Gen. 31:48). Scripture states elsewhere in reference to this verse: And crushed Balaam’s foot against the wall (Num. 22:25). The heap alluded to in our text was the very wall at which Balaam violated the promise he had made to Jacob, as it is said: I will not pass over this heap to harm you (Gen. 31:52). Balaam and Laban were one and the same,¹³Sanhedrin 105a. See Ginzberg, Legends of the Jews 6:123. for it is said of him: An Aramean was destroying my father (Deut. 26:5). Balaam was called an Aramean, because he desired to annihilate Israel, as is said: Come, execrate Israel (Num. 23:7). Hence, it was the very wall that had borne witness to the oath that he had made that called him to account, as is written: The hand of the witness shall be first upon him (Deut. 17:7). And Jacob swore by the Fear of his father, Isaac (Gen. 31:53). This righteous man did not swear by the name of the king, but rather on the life of his father. He did it just as a man who desires to prove the truth of this remarks says: “I swear by the life of my father.” He swore this oath only out of respect, as is written: A son shall honor his father (Mal. 1:6).