The ruling on whoever forgot to say the Talbiyyah
Question :
A Hajj pilgrim assumed Ihram from the Miqat but in the Talbiyyah he forgot to say: "Labbayk Umratan Mutamat ti'an biha ilal-Hajj" (I am here at Your service to perform 'Umrah combining it with Hajj as At-Tamattu). Shall he complete his rites of Hajj and Umrah as a Mutamatti"? What is due upon him if he removed his Ihram from his 'Umrah then assumed Ihram for Hajj from Makkah?
Answer:
If he intended to perform 'Umrah when he assumed Ihram, but he forgot the Talbiyyah while he was intending 'Umrah, his ruling is the ruling of whoever says the Talbiyyah. He performs Tawaf, Sa'y, gets his hair cut and removes his Ihram. It is legislated for him to say the Talbiyyah on the road (to Makkah). If he does not say the Talbiyyah, there is no sin on him, because the Talbiyyah is Sunnat Mu'kkadah - a compulsory Sunnah (i.e., not obligatory). Thus, he makes Tawaf, Sa'y, gets his hair cut and he considers it an 'Umrah, because he intended to perform 'Umrah. However, if he is in Ihram and he intends to perform Hajj, and the time is abundant, it is better for him to cancel his Hajj and change his intention to 'Umrah. Then he makes Tawaf, Sa'y, gets his hair cut and removes his Ihram - and all praise is due to Allâh. In this case his ruling is the ruling of those who are performing Umrah and Hajj together as At- Tamattu'.
Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 4 Page 94