Genesis 47:29

Put thy hand under my thigh, i.e. swear to me, as Genesis 47:31, that thou wilt do what I am now desiring of thee; See Poole on "Genesis 24:2". He requires this, not out of any distrust of Joseph's promise, but partly, as a more solemn protestation of his right to and affection for that promised land; partly, us a motive to all his children to have their minds and hearts there, even when their bodies were in Egypt; and partly, to give Joseph an argument and excuse to Pharaoh, that he might more willingly permit Joseph to fulfil his father's desire, because of his own oath. And deal kindly and truly, or, that thou wilt deal; as the Hebrew vau joined with the future tense is elsewhere used, as Psalms 24:7, Psalms 35:24 51:15. Kindly in promising, and truly in performing thy promise.