Does prayer become invalid by interrupting it immediately after the opening takbeer – due to doubt about the validity of the takbeer – then performing the takbeer again?

Whoever doubts having uttered the opening "Allahu Akbar" (takbirat al-ihram) or its validity, his prayer has not commenced, and he must restart it if it was an obligatory prayer. This applies if the doubt occurred before completing the act of worship and if the person was not prone to obsessive doubts (waswas). Thus, restarting the prayer was correct, and interrupting a prayer whose opening takbir is doubted does not affect the validity of the restarted prayer. All of this applies to ordinary doubt. However, if doubt becomes frequent and turns into obsessive doubt (waswas), then one must disregard it.