Can he enter ihraam for ‘umrah only then form the intention to do Hajj from Makkah?

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Check below answers in case you are looking for other related questions:
Description of Hajj
Brief description of Hajj for oneself and on behalf of another, and the kinds of Hajj

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Related Answers:
Specifying the name of the person on whose behalf the sacrifice is being offered
The one who is doing tamattu‘ must do sa‘i twice – once for ‘umrah and once for Hajj
It is not permissible to change the intention of ihraam from Qiraan to Ifraad
Description of Hajj
Brief description of Hajj for oneself and on behalf of another, and the kinds of Hajj

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