Since Almighty God made all human beings swear to His Unique Divinity and Lordship when He created Adam (see Qur'an 7:172), this oath is printed on the human soul even before it enters the mother's foetus. So when a child is born, it has with it a natural belief in God.
This natural belief is called in Arabic the "fitrah". If a child were left alone, it would grow up aware of Almighty God in His Unity, but the pressures of their environment affect all children.
The Prophet Muhammad - the Final Messenger of God (saws), reported that God the Exalted said:
"I created My servants in the right religion, but the devils made them go astray." Sahih Muslim
The Messenger of God (saws), also said:
"Each child is born in a state of fitrah, but his parents make him a Jew or a Christian." (Bukhari and Muslim)
It is obligatory for all Muslims to bind ourselves to the teachings of the Book of God (i.e. By the light of these teachings we should live and their guidance we should adopt in all of our affairs. In regards to this, Almighty God the Most High and Exalted, says in the Qur'an:
"It is not fitting for a Believer, man or woman, when a matter has been decided by God and His Messenger to have any option about their decision: if anyone disobeys God and His Messenger he is indeed on a clearly wrong Path." (Qur'an 33:36)
And additionally, God, the Most High and Exalted, has said:
"And whatsoever the Messenger gives you, take it, and whatsoever he forbids you, abstain (from it)! and fear God. Verily, God is severe in punishment." (Qur'an 59:7)
The fitrah is the natural inclination to worship God alone, and it includes compliance with what God and His Messenger explained to be from the characteristics of fitrah. The acts of fitrah are specific features, which God has created in man and found within his natural tendency to like as well as to dislike what contradicts these acts.
The great Islamic scholar al-Sayyuti said: "The best explanation of fitrah is that it is the Sunnah (way) of all of the Prophets which is in agreement with (all of) the revealed Laws, indicating that it is a response to naturally created inclinations. In the Holy Qur’an, Almighty God, the Most High and Exalted, has identified the pure fitrah with which He created mankind:
"So set your purpose for religion as a man upright (hanifan) by nature (fitrah) - the nature (fitrah) framed by God, in which He created mankind. There is no altering (the Laws of ) the creation of God." (Qur'an 30:30)
In this verse, God Most High also identifies the fitrah with the way of the hanifa, which means the way of Pure Monotheism as practiced by Abraham, peace be upon him. The religion of Abraham and all of the prophets, peace be upon them all, was one of the true fitrah, in which they worshipped Almighty God alone without intermediaries or an incarnate "Saviour".
Since it is obligatory on Muslims to following the commands of the Prophet Muhammad (saws) , as the previously mentioned verses from Qur'an clearly state, all Muslims should make every effort to comply with and maintain the characteristics of fitrah as described by God's Messenger (saws), when he said:
"Five practices are characteristics of the fitrah: circumcision, shaving the pubic hairs, cutting the moustaches short, clipping the nails and plucking the hair of the armpits." (Bukhari and Muslim)
This same saying of God's Messenger is further elaborated upon in Sahih Muslim, where 'Aisha (ra), reports that the Messenger of God (saws), said:
"Ten are the practices of fitrah: clipping the moustache, letting the beard grow, using the tooth-stick (siwaak), snuffing water up the nose, cutting the nails, washing the finger joints, plucking the hair under the armpits, shaving the pubic hairs and cleaning one's private parts with water." The narrator said: 'I have forgotten the tenth, but it may have been rinsing the mouth.'
In regards to the circumcision, it is desirable that it be done on the seventh day after the birth of the child. It is reported that the Prophet Muhammad (saws), circumcised Hasan and Hussein, the two sons of Fatimah and 'Ali, on the seventh day after their birth. However, there is no harm in delaying the circumcision until later.
It is reported in Sahih al-Bukhari that Prophet Abraham (as), performed his own circumcision at the age of eighty. In regards to Abraham, Almighty God the Most High says in the Holy Qur'an:
"And (remember) when his Lord tried Abraham with (His) commands, and he fulfilled them . . . " (Qur'an 2:124)
"And who forsakes the religion of Abraham save him who fools himself? Verily We chose him in the world, and lo! in the Hereafter he is among the righteous. (Qur'an 2:130)
The trimming of the moustache means that it should be trimmed so that none of it hangs over the lip. Additionally, the beard must be left alone so that it grows thickly on the face. The Prophet Muhammad (saws), whom we are ordered to follow, made it clear that the Muslim male must let his beard grow.
Ibn 'Umar (ra), said:
"The Messenger of God, may God bless him and give him peace, ordered us to trim closely the moustache and leave the beard as it is." (Bukhari and Muslim)
Abu Huraira (ra), reported that the Messenger of God (saws), said:
"Trim closely the moustache and grow the beards, and oppose the Magians (fire-worshippers)." (Muslim)
According to the Sunnah of God's Messenger, Muslims should pluck the hair in their armpits and shave their pubic hairs. If they feel that they cannot pluck the hairs of the armpits, they can shave them or remove them in another fashion.
The nails of the hands and the feet should also be trimmed. It is best to start with the right hand and then continue with the left, and then move to the right foot and finish with the left foot. It is reported that the Prophet Muhammad (saws), liked to do it in this manner.
Muslims who do these acts with the sole intention of following the Sunnah of God's Messenger (saws), will be rewarded by God Most High.
It is reported in both Sahih al-Bukhari and Sahih Muslim that the Messenger of God (saws), said: "Whoever turns away from my Sunnah is not of me."
source: mission islam