Ibn Umar (Radi Allaahu Ta’ala Anhu) narrated the Holy Messenger of ALLAH said, Religion is the sum total of five things (all of them are fundamental) none of them is tenable without the other in the sense that it may completely relieve one from the Hell: testifying that there is no deity but ALLAH, belief in His angels, His Messenger, Paradise and Hell and that the dead will be raised to render their accounts. This is one of the things. Then there are five Salaah (daily) which constitute one of the pillars of Islam. Without Salaah ALLAH will not accept even Eeman (faith). Zakat is atonement for sins. Without Zakat ALLAH, will not accept Eeman and Salaah.
Then if one who has performed these duties but fails to fast intentionally and without excuse during the month of Ramadan, ALLAH will accept neither his Eeman, nor Salaah, nor Zakat. If one has discharged all these duties and has the means to perform Hajj but did neither perform it himself (during his lifetime) nor any of his relations do so on his behalf then neither his Eeman, nor his Salaah, nor his Zakat, nor his fasting will be acceptable to ALLAH. Acceptability means that due to any deficiency in the performance of any of the fundamentals of Islam, the remaining (good) actions will not be enough for immediate relief from the Hell. [Al-Hiliya, Tarjuman-us-Sunnah]