All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Obviously, this game (poker) involves two violations of Sharia:
If it is gambling where the player loses or wins money in return for playing, then it is Haram (Forbidden). The evidence on this is that Allah the Almighty Says: "O ye who believe! Intoxicants and gambling, (dedication of) stones, and (divination by) arrows, are an abomination,- of Satan’s handwork: eschew such (abomination), that ye may prosper." {Al-Mai`dah, 90}.
If it isn`t gambling for money, then it is a practice on gambling and an encouragement to commit the unlawful in a recreational manner. There is no doubt that this is also Haraam, because Islam forbids imitating the disbelievers and the evil doers. This is attested to in the following verse: "Now then, for that (reason), call (them to the Faith), and stand steadfast as thou art commanded, nor follow thou their vain desires…" {Al-Shura, 15}.
In the authentic Sunnah, the Prophet (PBUH) says, "Whoever imitates any people (in their actions) is considered to be one of them." {Abu Dawoud}.Our scholars have forbidden imitating the people of sin and evil even in something that is lawful in essence. This is in order to put an end to such thing and discourage people from doing it. This applies to every game, which is lawful in essence, but played in the form of gambling.
The eminent scholar Ibn Hajar Al-Haithami (May Allah have mercy on him) says: "When cups of coffee are handled as glasses of wine, this prohibited." {Al-Sunan Al-Kubra, vol.4/pp.361}. And Allah The Almighty Knows Best.