Why is gambling haram?

Allah says in the Qur’an:

They ask thee concerning wine and gambling. Say in them there is great sin and some benefit for men. The sin is greater than the benefit.

(Surah al-Baqarah 219)

Abu Hurayrah narrates that the prophet (Allah bless him and give him peace) forbade transaction determined by Hasah and Gharrar. (Muslim)

Hasah is a transaction contracted on chance. Hasah linguistically means pebble or small stone. An example of hasah is when a person says to a customer ‘I will sell you the items on which your pebbles fall’ it is clear that the transaction is based on an unknown outcome.

Tafsir Uthmani V.1 pg 119

The risk involved in gambling is outside the control of players, therefore the result of the outcome is a matter of chance. The prohibition of gambling is regardless of the probability of the outcome. The probability of a head or tale when a coin is tossed is 1/2; where as the probability of picking 7 numbered balls out of 50 33232 billion 930 million 569 thousand and 600! (1/33232930569600). Since both these examples are based on chance the ‘odds’ probability on the outcome whether high or low is irrelevant.

Gharar is defined as an exchange in which there is an element of ‘deception’ through the ignorance of the goods or price.

Gambling in a more limited sense it means an effort to gain something of value by risking the loss of something of value as a matter of chance. (Colliers Encyclopaedia V.10 pg 561)

(‘The National Lottery Exposed’ by M.Siraj Yusuf Lambat)