Al-jawab billahi at-taufeeq (the answer with Allah’s guidance)
1) To gamble is forbidden in Islam and a major sin. (Al Kabair Pg. 96)
Allah Ta’ala says,
“They ask you (O Muhammad ) concerning alcoholic drink and gambling. Say: “In them is a great sin, and (some) benefit for men, but the sin of them is greater than their benefit.” And they ask you what they ought to spend. Say: “That which is beyond your needs.” Thus Allah makes clear to you His Laws in order that you may give thought.” (2:19)
“O you who believe! Intoxicants (all kinds of alcoholic drinks), gambling, AlAnsab , and AlAzlam (arrows for seeking luck or decision) are an abomination of Shaitan’s (Satan) handiwork. So avoid (strictly all) that (abomination) in order that you may be successful.” (5:90)
“Shaitan (Satan) wants only to excite enmity and hatred between you with intoxicants (alcoholic drinks) and gambling, and hinder you from the remembrance of Allah and from As-Salat (the prayer). So, will you not then abstain?” (5:91)
Prophet (Sallallahu Alaihi Wasallam) said, “Some people spend Allah’s wealth (i.e. Muslim’s Wealth) in an unjust manner, such people will be put in the (Hell) fire on the day of resurrection.” (Bukhari, Ahmad)
He (Sallallahu Alaihi Wasallam) also said, “The one who invites his companions: Come let us gamble”, should (expiate his sin) by giving in charity.” (Bukhari)
Please view this: http://www.inter-islam.org/Prohibitions/prohibitdex.htm
2) There are no specific Du`as to stop someone from gambling.
3) The Haraam money should be given to the poor without the intention of reward.
And Only Allah Ta’ala knows best.
Moulana Qamruz Zaman