It is stated in a hadith-i sharif quoted by Tabarani that a person who does not observe any of the following ten essentials of Islam is in  loss:  

1. Saying “La ilaha ill-Allah Muhammadun Rasul-Allah”

In order to become a Muslim, it is necessary to say this Kalimat at-tawheed with a heartfelt belief in it. When one becomes a Muslim, it will primarily be fard [obligatory] for one to know and believe in the meaning of the phrase “La ilaha ill-Allah Muhammadun Rasul-Allah.” This phrase is called Kalimat at-tawheed. The brief meaning of it: There is no ilah except Allah, and Muhammad (‘alaihis-salam) is His Prophet. Belief in the Prophet of Allah means to accept, believe, and like all of what he communicated.

It is declared in hadith-i sharifs:

(Of the deeds, the valuable one is saying “La ilaha ill-Allah.”) [Hakim]

(Renew your iman by  often saying “La ilaha ill-Allah.”) [Tabarani]

(A person who says “La ilaha ill-Allah” attains salvation from predicaments and afflictions.) [Bazzar]

2. Keeping up five daily salats

Those who perform salats correctly are considered to express their gratitude for all the countless blessings of Allahu ta’ala. As the saying goes, “Salat embraces all kinds of gratitude.” It is the pillar of the religion, so people who ignore it have torn down their religion. The Qur’an al-karim says (what means):

(The rewards of those are with their Rabb who believe and do righteous deeds, perform salat and give zakat. They will have no fear, nor will they suffer sorrows.) [Surat-ul-Baqara 277]

3. Giving zakat

Zakat has been commanded with salat in many verses of the Qur’an al-karim. The following is declared in hadith-i sharifs:

(Let him who believes in Allah and His Messenger give the zakat of his property.) [Tabarani]

(By giving zakat, you reach perfectness in being a Muslim.) [Bazzar]

(Allah curses him who does not give zakat.) [Nasai]

4. Fasting

It is fard [obligatory] to fast every day of the month of Ramadan. (Surat-ul-Baqara 185)

The following hadith-i sharifs state: 

(He who fasts is my friend; he who does not fast is my enemy.) [Bayhaqi]

(He who dies after fasting in the month of Ramadan will go to Paradise.) [Daylami]

5. Performing the hajj [major pilgrimage]

For people who have money enough to go to and come back from the blessed city of Mecca besides the property sufficient for the subsistence of their family they leave behind until they come back, it is fard to perform tawaf around the Ka’ba and to perform waqfa on the plain of ‘Arafat once in their lifetimes.

The Qur’an al-karim says (what means):

(Pilgrimage to the Baitullah [the House of Allah] is Allah’s right upon those who are able to journey there.) [Surat-u Al-i ‘Imran 97]

It is reported in hadith-i sharifs:

(All the sins of a person whose hajj has been accepted are forgiven.) [Bayhaqi]

(The thawab given for the property spent on the way of hajj is seven hundred times as much of it.) [Bayhaqi]

(If a person dies on the way to Makka for hajj or on the way back, scales will not be set up for him in the next world. He will not be called to account, and all his sins will be forgiven.) [Isfahani]

6. Performing jihad

It is an important act of worship. The Qur’an al-karim says (what means):

(Perform jihad in the way of Allah, so that you attain salvation.) [Surat-ul-Maida 35]

It is declared in hadith-i sharifs:

(The best of people is the one who performs jihad with his life and property.) [I. Ahmad]

(The best jihad is performing the fards [obligatory acts of worship].) [Tabarani]

7. Amr-i ma’ruf

It means to enjoin and spread what is good. A hadith-i sharif says:

(He who does not enjoin what is good and does not forbid what is evil when he is able to do so is not in our community.) [Tirmidhi]

8. Nahy-i munkar

It means to forbid what is evil. It is declared in a hadith-i sharif:

(The mujahid higher than a martyr is the one who enjoins what is good and forbids what is evil.) [I. Ghazali]

9. Joining the jama’ah

Jama’ah [the community of Muslims] brings about Allah’s Compassion; separation from jama’ah causes His Torment. A hadith-i sharif says:

(He who separates from jama’ah falls flat on his face into Hell.) [Tabarani]

10. Ta’at

They are actions that Allahu ta’ala likes. A Muslim who practises them earns thawab. On the other hand, a person who does not do any deeds that Allahu ta’ala likes will certainly suffer a great loss.   

The Qur’an al-karim says (what means):

(Make dhikr of Me [by doing ta’at], and I, too, will make dhikr of you [with My Compassion].) [Surat-ul-Baqara 152]

A hadith-i sharif, too, states:

(Allahu ta’ala does not like a person who is in negligence of carrying out ta’at.) [Daylami]