A: Although uttering out loud the intention to do a certain act of worship is not Mashru` (Islamically acceptable) because of lack of evidence supporting it, it is Mustahab (desirable) to make the intention to perform Hajj or `Umrah in an audible voice, saying: "Labbayka hajjah, or Labbayka `Umratan, or Labbayka `Umratan wa hajjan (O Allah! Here I am at Your service to perform Hajj, or O Allah! Here I am at Your service to perform `Umrah, or O Allah! Here I am at Your service to perform `Umrah and Hajj). It is preferable for the pilgrim who arrives in Makkah during the months of Hajj to form the intention to perform `Umrah only. In this case, he will perform Tawaf (circumambulation around the Ka`bah), Sa`y (going between Safa and Marwah during Hajj and `Umrah), shave or cut the hair and finally perform Tahalul (removal of the ritual state for `Umrah). On the eighth of Dhul-Hijjah, he may form the intention to perform Hajj if he does not bring Hady (sacrificial animal offered by pilgrims) along with him. This is because the Prophet (peace be upon him) ordered his Sahabah (Companions) to do that in the year of the Farewell Pilgrimage and he (peace be upon him) said: "Take your Hajj rituals from me."
[Fatawaa Shaykh Ibn Baaz - Alifta.net]
See Also: Intention is made in the heart