Islam is built on five

Prayer is the second pillar of Islam, right after the testimony of faith.

Narrated by Abdullah ibn Umar

Islam is built on five: testifying that there is no god but Allah and that Muhammad is the Messenger of Allah, establishing the prayer, giving the zakah, Hajj to the House, and fasting Ramadan.

Sahih al-Bukhari 8, Sahih Muslim 16

What this hadith teaches

The Prophet ﷺ compares Islam to a building resting on five pillars. Prayer comes straight after the shahadah, which shows its rank: without it the building cannot stand.

Reference and grade

Grade
Sahih: agreed upon by al-Bukhari and Muslim
Narrator
Abdullah ibn Umar

The hadith in Arabic نص الحديث

بُنِيَ الإِسْلاَمُ عَلَى خَمْسٍ شَهَادَةِ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ، وَإِقَامِ الصَّلاَةِ، وَإِيتَاءِ الزَّكَاةِ، وَالْحَجِّ، وَصَوْمِ رَمَضَانَ

Arabic text of Sahih al-Bukhari 8, as given on sunnah.com.