Hadith: Islam is built upon five (pillars)

عَنِ أَبي عبدِ الرَّحمنِ عبدِ اللهِ بْنِ عُمَرَ بن الخَطَّابِ رَضِيَ اللَّهُ عَنْهُمَا قَالَ: سَمِعتُ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ يَقُولُ: " بنِيَ الإِسْلاَمُ عَلَى خَمْسٍ: شَهَادَةِ أَنْ لاَ إِلَهَ إِلَّا اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ، وَإِقَامِ الصَّلاَةِ، وَإِيتَاءِ الزَّكَاةِ، وَحَجِّ البَيتِ، وَصَوْمِ رَمَضَانَ".
[صحيح] - [متفق عليه]

Abu ‘Abdur-Rahmān ‘Abdullah ibn ‘Umar ibn al-Khattāb (may Allah be pleased with him and his father) reported: "c2">“I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: ‘Islam is built upon five (pillars): testifying that there is no god worthy of worship but Allah and that Muhammad is the Messenger of Allah, establishing the prayer, paying Zakah, performing Hajj and fasting the month of Ramadan.’”
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

‘Abdullah ibn ‘Umar ibn al-Khattāb (may Allah be pleased with and his father) reported: "c2">“I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: ‘Islam is built upon five (pillars). Meaning: Islam is like a structure, and those five are like the supportive pillars that make it firmly established. The first one is to testify that there is no god worthy of worship but Allah, which means that there is no deity that is truly worthy of worship but Allah. It is the word of Tawhīd (Islamic monotheism) without which one’s Islam is not valid. Verbalizing it is a must, same as understanding its meaning and acting upon its requirements. And to testify that Muhammad is the Messenger of Allah, which entails believing him in all what he conveyed of information authentically attributed to him, obeying his commands, avoiding what he forbade, and worshiping Allah only according to the way he ordained. The second is establishing the prayer, which is the most significant pillar second to the two testimonies of faith. They are five obligatory prayers to be performed daily, therefore, it is considered a strong relationship between the servant and his Lord. Establishing the prayer is to perform it on a regular basis. The third is to pay Zakah. It is a financial act of worship done once a year when one full lunar year has passed with the money liable to Zakah is in the possession of the owner, or when the fruits are ripe. Zakah’s benefits extend to others and are not limited to its doer. That is why it comes after prayer, preceding Hajj and fasting. Fourth: making Hajj to the Sacred House of Allah. It is a physical act of worship since the person performs it by his own body. It is permissible and valid to perform it on behalf of others in cases where authorization in Hajj is allowable. It is also a financial act of worship, considering the money and provision one needs for its journey. The fifth is fasting the month of Ramadan. Fasting is a bodily act of worship that is not extending to others. It is all about refraining from certain acts (i.e. the invalidators of fasting) with an intention. Fasting is obligatory for one month only, namely the month of Ramadan. Islam is not valid without fulfilling the first and the second pillars. Jābir (may Allah be pleased with him) reported: “I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: ‘Between a man and falling into polytheism and disbelief is to abandon the prayer.’” [Narrated by Muslim] The Hadīth is to be understood according to its apparent indication, as there are no authentic reports in this regard to contradict it. There were some deductions not conforming with the understanding of the righteous predecessors that clashed with its apparent indication. However, the Companions (may Allah be pleased with them) unanimously agreed on the disbelief of the one who abandons the prayer, as authentically reported from them. ‘Abdullah ibn Shaqīq al-‘Aqīli said: "c2">“The Companions of Muhammad (may Allah’s peace and blessings be upon him) did not believe that the abandonment of any action constituted disbelief except the abandonment of prayer.” [Narrated by At-Tirmidhi in Al-Jāmi‘ and Al-Marwazi in Ta‘zhīm qadr as-salāh] As for the other three pillars, if one abandons them without a valid excuse, his Islam is deficient and he is in extreme error, and exposed to great danger. However, he is not considered a disbeliever on account of such abandonment, based on the indication of other texts.