Prayer is a form of worship and worship is the highest form of humility and homage, before God. As to its importance, it is enough to state that worship is the purpose behind the creation of all beings and the mission of the prophets.
Shi'a Islam allows for the combination of the 5 daily prayers (salah) into three times - the exact why in which the Prophet of Islam Prophet Muhammad (pbuh) taught it. Whereas the majority of other schools within Islam say that this is only permissible during journeys or in state of danger or war.
“Establish regular prayers at the sun’s decline till the darkness of the night, and the recital of the Qur’an in the morning prayer; for the recital of the dawn is most witnessed.” (17:78)
All Muslims observe the five daily prayers, but Shias believe these five prayers can be prayed at three (rather than five) different times - as stated in the Holy Qur’an,
“Establish regular prayers at the sun’s decline till the darkness of the night, and the recital of the Qur’an in the morning prayer; for the recital of the dawn is most witnessed.” (17:78)
How many prayer times are mentioned in this verse? Yes, three, not five: “Sun’s Decline, Darkness of the Night, and the Morning Prayer.”
What did the Prophet (pbuh) do?
Now, what did the Prophet (S) do? Here’s what Ibn Abbas, one of the most famous narrators, says according to the Musnad of Ibn Hanbal (One of the books of tradition):
"The Prophet (S) prayed in Madina, while residing there, not travelling, seven and eight (this is an indication to the seven Raka’t of Maghrib and Isha combined, and the eight Raka’t of Zuhr and `Asr combined)."
Musnad al-Imam Ibn Hanbal, vol. 1, page 221.
Also, in the Muwatta’ of Malik (Imam of Maliki sect), vol. 1, page 161, Ibn Abbas says:
"The Prophet (S) prayed Zuhr and `Asr in combination and Maghrib and Isha in combination without a reason for fear or travel."
As for Sahih Muslim, see the following under the chapter of "Combination of prayers, when one is resident",
Ibn Abbas reported: The messenger of Allah(may peace be upon him) observed the noon and the afternoon prayers together, and the sunset and Isha prayers together without being in a state of fear or in a state of journey.
Sahih Muslim, English version, Chapter 250, Tradition #1515
Ibn Abbas reported that the messenger of Allah(may peace be upon him) combined the noon prayer with the afternoon prayer and the sunset prayer with the Isha prayer in Medina without being in a state of danger or rainfall. And in the hadith transmitted by Waki(the words are): "I said to Ibn Abbas: What prompted him to do that? He said: So that his(prophet’s)Ummah should not be put to (unnecessary) hardship."
Sahih Muslim, English version, Chapter 250, Tradition #1520
Abdullah b. Shaqiq reported: Ibn Abbas one day addressed us in the afternoon(after the afternoon prayer) till the sun disappeared, and the stars appeared, and the people began to say: Prayer, prayer. A person from Banu Tamim came there. He neither slackened nor turned away, but (continued crying): Prayer, prayer. Ibn Abbas said: May you be deprived of your mother, do you teach me sunnah? And then he said,
I saw the messenger of Allah(may peace be upon him) combining the noon and afternoon prayers and the sunset and Isha prayers. Abdullah b. Shaqiq said: Some doubt was created in my mind about it. So I came to Abu Huraira and asked him(about it) and he testified his assertion.
Sahih Muslim, English version, Chapter 250, Tradition #1523
Abdullah b. Shaqiq al-Uqaili reported: A person said to Ibn Abbas(as he delayed the prayer): Prayer. He kept silent. He again said: Prayer.
He again kept silent, and he cried: Prayer. He again kept silent and said: May you be deprived of your mother, do you teach us about prayer? We used to combine two prayers during the lifetime of the messenger of Allah(may peace be upon him).
Sahih Muslim, English version, Chapter 250, Tradition #1524
Ibn Abbas reported: The messenger of Allah(may peace be upon him) observed the noon and afternoon prayers together in Medina without being in a state of fear or in a state of journey. Abu Zubair said: I asked Sa’id(one of the narrators) why he did that. He said, 'I asked Ibn Abbas as you have asked me, and he replied that he(the Holy prophet) wanted that no one among his Ummah should be put to (unnecessary) hardship.
Sahih Muslim, English version, Chapter 250, Tradition #1516
Ibn Abbas reported that the Messenger of Allah(may peace be upon him) observed in Medina seven (rakahs) and eight(rakahs), i.e., (he combined) the noon and afternoon prayers(eight rakahs) and the sunset and Isha prayers(seven Rakahs).
Sahih Muslim, English version, Chapter 250, Tradition #1522
Now, who is it that follows the customs and tradition of the Prophet (S)??? The Shi’a who follow it to the letter, or the Sunnis who don’t even acknowledge the traditions in their own books? This is a SIGN for those who reflect!
Furthermore, Allah (SWT) continually reminds us in the Qur’an that Islam was revealed to make your life easier, not more difficult. How then, can one work, eat, sleep, study, etc... with five prayers a day in five different times? You pray Maghrib, and an hour later, you pray Isha. Is this convenient, say for doctors in a surgery room? Believe me, if the Sunnis followed what the Prophet (S) did (five prayers in three times a day), many people would be praying today.
Question and ask for the truth, and if you are honest and sincere, Allah (SWT) will guide you.