The first pillar is “bearing witness to the existence of one God” (Quran 3:18, Sahih Bukhari Volume 1 Book 2, No 7). The Quran further demands that no partners should be attributed to the one God and that He it is who created the heavens and the earth (Quran 25:2). This is also known as the Shahada, and the notion of bearing witness to the existence of one God as Tauheed. It can be said that the belief and practicing of this pillar is the first identification of a Muslim from a non-Muslim. Surat al- Ikhlas (Purity of Faith; Quran 112:1-4) affirms this strongly by stating … “ Say: He is Allah, The One, Allah, the eternal, Absolute, He begetteth not, Nor is he begotten; And there is none Like unto Him.” These verses sum up the first pillar by its demand to the adherence of one god and warning against the association of partners to the one God. The importance of this concept is affirmed in several of the ahadith of the prophet (PBUH) as well. For example in the ahadith collection of Sahih Bukhari (Volume 9, Book 93, Number 471) he reports: Narrated Abu Said Al-Khudri: A man heard another man reciting (in the prayers): 'Say (O Muhammad): "He is Allah, the One." (112.1) And he recited it repeatedly. When it was morning, he went to the Prophet and informed him about that as if he considered that the recitation of that Surat by itself was not enough. Allah's Apostle said, "By Him in Whose Hand my life is, it is equal to one-third of the Quran."

Its link to health would be the fact that a Muslim by believing and bearing witness to the existence of one God is starting on the first step on the ‘Islamic health continuum’ (indirect to direct) through the salutogenic mechanism by making a religious commitment to himself first and to the community he is in.

Reference:

Khan M. M.(2001). Sahih Bukhari Translation. Muslim Student Association, University of Southern California. Web site