Maisir

In Islam, gambling (ميسر or قمار qimâr) is forbidden (haraam). Maisir is totally prohibited by Islamic law (shari'a) on the grounds that "the agreement between participants is based on immoral inducement provided by entirely wishful hopes in the participants' minds that they will gain by mere chance, with no consideration for the possibility of loss".

Definitions
Both qimar and maisir refer to games of chance, but qimar is a kind (or subset) of maisir. Author Muhammad Ayub defines maisir as "wishing something valuable with ease and without paying an equivalent compensation for it or without working for it, or without undertaking any liability against it by way of a game of chance", Another source, Faleel Jamaldeen, defines it as "the acquisition of wealth by chance (not by effort)". Ayub defines qimar as "also mean[ing] receipt of money, benefit or usufruct at the cost of others, having entitlement to that money or benefit by resorting to chance"; Jamaldeen as "any game of chance".

In scripture
It is stated in the Quran that games of chance, including maisir, are a "grave sin" and "abominations of Satan's handiwork". It is also mentioned in ahadith.

"They ask you about wine and gambling. Say: 'In them both lies grave sin, though some benefit, to mankind. But their sin is more grave than their benefit.'"

- Qur'an 2:219

"O believers, wine and gambling, idols and divining arrows are an abhorrence, the work of Satan. So keep away from it, that you may prevail. Satan only desires to arouse discord and hatred among you with wine and gambling, and to deter you from the mention of God and from prayer. Will you desist?"

- Qur'an 5:90-91

"Narrated Abu Huraira: The Prophet said, "Whoever swears saying in his oath. 'By Al-lāt and al-‘Uzzá,' should say, 'None has the right to be worshipped but God; and whoever says to his friend, 'Come, let me gamble with you,' should give something in charity.""

- Sahih Bukhari, Book 78 (Oaths and Vows), hadith 645