The Prophet, sallallaahu ‘alayhi wa sallam, judged that any disbeliever becomes a Muslim as soon as he professes the two testimonies of faith.
How can we reconcile that Hadeeth and the following two Hadeeths:
1- “I was commanded to fight people until they testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is the Messenger of Allaah, establish prayer and pay Zakaah (obligatory alms).”
2- The famous Hadeeth of Jibreel (Gabriel), may Allaah exalt his mention, in which the Prophet, sallallaahu ‘alayhi wa sallam, included the five pillars and not only the two testimonies of faith, in the definition of Islam.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.

The Sharee’ah ruling on this issue cannot be deduced from one or two texts only. Rather, all related texts must be combined and reconciled to remove any ambiguity or uncertainty.

There are Sharee’ah texts that signify that a disbeliever becomes a Muslim as soon as he professes the two testimonies of faith. It was narrated on the authority of Usaamah ibn Zayd that the Prophet, sallallaahu ‘alayhi wa sallam, sent a group of Muslims to a tribe of polytheists. When the group reached a place called Al-Hurayqaat, Usaamah attacked a man among the army of polytheists, and when he raised his sword the polytheist uttered, “Laa illaaha illallaah (There is no god truly worthy of worship except Allaah)”.  Nevertheless, Usaamah ibn Zayd killed the man. When they returned, Usaamah informed the Prophet, sallallaahu ‘alayhi wa sallam, about the man and what he had done to him. The Prophet, sallallaahu ‘alayhi wa sallam, was outraged and said to Usaamah : “You killed him after he had said that there is none worthy of worship except Allaah?”  Usaamah responded by saying that the man uttered this only out of fear that he might be killed. The Prophet, sallallaahu ‘alayhi wa sallam, censured him saying: “Did you slit open his heart to know why he really said it?”  The Prophet, sallallaahu ‘alayhi wa sallam, went on repeating this to Usaamah until he wished that he had embraced Islam only on that day. [Muslim].  This Hadeeth proves that a person is considered a Muslim as soon as he professes the two testimonies of faith.

However, there are other Sharee’ah texts that signify that whoever professes the two testimonies of faith is nonetheless required to implement the pillars of Islam, i.e., prayer, Zakah, fasting, pilgrimage, etc.  These are some of the texts:

Allaah Knows best.