If one intends to enter the state of Ihram but does not recite the Talbiyah, he does not become a Muhrim. Intention alone is not sufficient for entering the state of Ihram for Hajj, and one does not enter the state of Ihram merely by intention; rather, it is necessary to recite the Talbiyah or something that serves as a substitute for it, or to imitate the camel while proceeding. The Prophet (peace be upon him) said to Aisha (may Allah be pleased with her): "So perform Ghusl and then declare your intention for Hajj" [in Sahih Muslim 2: 881]. His command is obligatory, and the relied-upon opinion is that one becomes a Muhrim by intention, but at the time of reciting the Talbiyah, just as one begins prayer by intention but at the time of Takbir, not just by the Takbir. See: I'laa as-Sunan 10: 42, and Al-Maslak Al-Mutqassit p. 100.