Is it better to make the intention for prayer while uttering the opening takbīr, or is it permissible to do so before it?

Intention (niyyah) is a condition for the validity of prayer, and its place is the heart. The intention may coincide with the Takbirat al-Ihram (the opening 'Allahu Akbar') or precede it. Some scholars have permitted a long interval between the intention and the prayer, as long as the intention is not revoked, because the ruling of the intention remains valid unless one intends to revoke it.