Exodus 32:11 “Remember Abraham, Isaac and Jacob, your servants, to whom by yourself you swore and mad this promise”. From it we note that Moses pleads with God on the basis of the Promise he made to his earthly friends. Moses (indirectly) used their assistance to help him just as we do when we ask the saints to pray for us.
Intercession of the dead saints is further confirmed by the scriptures when we read that God himself says to Solom 1 Kings 11 “for your Fathers sake, However, I will not do this (take away his kingdom)during your life time but will tear it out of your Son’s hands. . . . for the sake of my servant David and for the sake of Jerusalem which I have chosen, I will leave your son one tribe”.
"Then, as before, I lay prostrate before the Lord for forty days and forty nights without eating and drinking, because of all the sin you had committed in the sight of the Lord…Yet once again the Lord listened to me. With Aaron too, the Lord was deeply angry, and would have killed him had I not prayed for him also at that time. Deutronomy 9:18-20
“…Grant our petition; pray for us to the Lord, your GOD, for all this remnant…Let the Lord your GOD, show us what way we should take and what we should do.” “Very well,” The prophet Jeremiah answered them: “I will pray to the Lord, your GOD, as you desire…” Jeremiah 42:2-4
“With all prayer and supplication, pray at every opportunity in the Spirit. To that end, be watchful with all perseverence and supplication for all the Saints: And for me, that speech may be given me, that I may open my mouth with confidence…” Ephesians 6:18-19