‘On that day there came to him Sadducees, those who say that there is no resurrection, and they asked him,'
Note the emphasis that it was ‘on the same day'. Thus the Pharisees, the Herodians and the Sadducees all approached Him to test Him on that day. All were out to bring Him down. We know little about the Sadducees for everything written about them was written by their opponents and therefore unreliable. But Matthew tells us that they did not believe in the resurrection. Josephus amplifies that by saying that they did not believe in the survival of either the soul or the body. It would seem that they also laid great emphasis on the Law of Moses (which was natural to a priestly party), although also recognising the prophets suitably interpreted. They did not believe in angels or spirits. Their emphasis was on the cult. The question that they approached Him with concerned the resurrection, and was probably a standard question with which they tripped up their opponents. It was based on the law of levirate marriage (Deuteronomy 25:5-10). Under that law if a man died childless his brother (or kinsman) was required to take his wife and produce children who would inherit the dead man's name, and his property. It was certainly practised early on for we have examples in Genesis 38:8 and in Ruth 1:11-13; Ruth 4:1-22 (the Greek rendering of Genesis 38:8 is reflected in Matthew' treatment of the subject), but we do not know how much it was actually practised in the time of Jesus. However, being in the Law it was certainly possible for it to be practised, and there is no reason to doubt that it was, especially if the wife was especially attractive or the inheritance large.