Read Luke 20:27-38
27 Then some Sadducees, who say that people will not rise from death, came to Jesus and said, 28“Teacher, Moses wrote this law for us: ‘If a man dies and leaves a wife but no children, that man’s brother must marry the widow so that they can have children who will be considered the dead man’s children.’ 29Once there were seven brothers; the eldest got married and died without having children. 30Then the second one married the woman, 31and then the third. The same thing happened to all seven—they died without having children. 32Last of all, the woman died. 33Now, on the day when the dead rise to life, whose wife will she be? All seven of them had married her.”
34 Jesus answered them, “The men and women of this age marry, 35but the men and women who are worthy to rise from death and live in the age to come will not then marry. 36They will be like angels and cannot die. They are the children of God, because they have risen from death. 37And Moses clearly proves that the dead are raised to life. In the passage about the burning bush he speaks of the Lord as ‘the God of Abraham, the God of Isaac, and the God of Jacob.’ 38He is the God of the living, not of the dead, for to him all are alive.” 
The Pharisees held the prophets to be authoritative scripture, and from the deduced the hope of resurrection. The Sadducees only held the first five books of the Bible to be authoritative. In these they found no hope of resurrection.
Jesus points out to them that Moses spoke of God as the God of Abraham – in the present tense, even though Abraham was long dead.