The eight commandment states that we are not to steal. Gambling is notorious for wasting the lives of those that engage in it. I cannot tell you how many people are in bankruptcy due to uncontrolled gambling debts. Society pays the cost of their sin by banks and credit card companies writing off their bad debt passing those costs on to others.
In addition, the third commandment says not to take the name of God in vain. This commandment prohibits the abuse of anything whereby God makes Himself known. The lottersy is a derivative of the lot. The Bible teaches that the lot belongs to the Lord and it has always been given to God's people as a means for knowing his will in deciding matters. Hence, the lottery is an abuse of something whereby God makes himself known and is therefore a violation of the third commandment.
Do you need a clear scripture stating "thou shalt not gambling? There is no text stating thou shalt not abort unborn babies either, but it is clearly a sin to do so.