As-Salaam alaykum
There are 5 fundamental observances revealed in the Prophet's hadith that constitute the pillars of Islam. He, Sallallahu alaihi Wasallam, said:--


"The religion of Islam is based on 5 fundamental principles: attesting that there
exists no deity but Allah, that Muhammad is His servant and His Messenger, praying,
fasting and pilgrimage."
(Bukhari and Muslim)

Related to this, our Prophet, Sallallahu alaihi Wasallam stated that the first act of worship that people will give an account of in the Hereafter is the prayer (Sallah), and the servant will be saved if he has fulfilled them and that he will be among the lost if he failed. (al-Tirmidhi)
In a certain hadith related by Umar Ibn al-Khattab, may Allah be pleased with him, people asked Allah's Messenger, Sallallahu alaihi Wasallam, which act of worship was most pleasing to Allah, Subhanahu Wa Ta'ala. The Prophet answered: "To offer prayer at the right time. Whoever abandons his prayer, he has no religion. The prayer is the pillar of the religion" ​(al-Bayhaqi).