The Prophet (pbuh) said: "Islam is built on five (pillars): the testimony that there is no god except Allah and that Muhammad is the Messenger of Allah, establishing prayer, giving Zakat, fasting the month of Ramadan, and pilgrimage to the (Sacred) House."
The pillars of Islam are the outward acts of worship that every Muslim must observe and believe in their obligation, otherwise, his belief is not valid, as Islam is built on them, and that is why they are called the pillars of Islam.
These pillars are as follows:
First Pillar: Shahādah (To bear witness that there is no god except Allah and that Muhammad is the Messenger of Allah).
Allah also says: {So know [O Muhammad], that there is no deity except Allah} [Ch. 47, Verse 19]
He also says: {There has certainly come to you a Messenger from among yourselves. Grievous to him is what you suffer; [he is] concerned over you and is kind and merciful towards the believers.} [Ch. 9, Verse 128]
The Shahādah that "There is no god except Allah" means that there is no deity worthy of worship but Allah.
The Shahādah that "Muhammad is the Messenger of Allah" means that it is obligatory to obey his orders, believe what he related, avoid what he forbade and warned against, and worship Allah only in the manner he instructed.
Second Pillar: Establishing Prayer (Salāh)
Allah also says: {And establish prayer} [Ch. 2, Verse 110]
Establishing prayer means performing prayer in the way prescribed by Allah and taught to us by His Messenger Muhammad (pbuh).
Third Pillar: Almsgiving (Zakat).
Allah also says: {and give Zakah} [Ch. 2, Verse 110]
Allah (SWT) made the Zakah obligatory to test the Muslim's faith, and as a way to express gratitude to his Lord for the wealth He has given him, and as a means to help the poor and needy.
The obligation of Zakah is fulfilled by giving it to the categories of people who are eligible to receive it.
Giving Zakah is obligatory if the money reached a certain amount. Its eligible recipients are eight categories of people that are mentioned in the Noble Qur'an, including the poor and needy.
Giving Zakah is an act of mercy and compassion; it purifies the Muslim's character and wealth, consoles the poor and needy, and strengthens the bonds of love and brotherhood in the Muslim community. Therefore, a good Muslim gives out Zakah wholeheartedly given the happiness he brings to other people by it.
The amount of Zakah is 2.5% of the saved wealth, whether it is gold, silver, cash money, or trade goods allocated for buying and selling for profit. Zakah is given only when the value of the saved wealth reaches the threshold amount and one full lunar year passed while it is in the person's possession.
Zakah is also obligatory on a certain amount of livestock such as camels, sheep and goats, if these animals graze naturally most of the year without their owner providing them with fodder.
Zakah is also obligatory on what the land produces of grains, fruits, minerals, and treasure if the certain amount is reached.
Fourth Pillar: Fasting the month of Ramadan
Allah also says: O you who believe, fasting is prescribed upon you as it was prescribed upon those who were before you, so that you may become righteous.} [Ch. 2, Verse 183]
Ramadan is the ninth month in the Hijri calendar. Muslims venerate it and hold it in special status, distinct from all the other months. Fasting this whole month is one of the five pillars of Islam.
Fasting Ramadan means worshiping Allah by abstaining from eating, drinking, and sexual intercourse from dawn to sunset during all days of the blessed month of Ramadan.
Fifth Pillar: Pilgrimage to the Sacred House of Allah (Hajj)
Allah also says: {Pilgrimage to the House is a duty owed to Allah upon all people who are able to make their way to it} [Ch. 3, Verse 97]
Hajj is due upon those who are able to make their way to it, once in a lifetime. Hajj is to head to the Sacred House and the Sacred Precincts in Makkah to perform certain acts of worship in a specific time frame. The Prophet (pbuh) performed Hajj, and so did the prophets before him. Allah Almighty commanded Ibrāhīm (Abraham, peace be upon him) to proclaim Hajj to people, as revealed in the verse that says: {And proclaim the pilgrimage to all people; they will come to you on foot and on every lean camel from every distant pathway.} [Ch. 22, Verse 27]