What is the ruling on intentional speech during prayer made by someone who knows it is forbidden and unnecessary for the prayer?

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The prayer is invalidated by unanimous consensus (Ijmā') if a person speaks intentionally while knowing they are in prayer, without intending to correct the prayer or for a necessary reason that permits speech. Scholars such as Ibn al-Mundhir affirmed this consensus. The evidence for the prohibition is the Hadith stating, 'Indeed, this prayer contains nothing suitable from the speech of people; it is only glorification, takbīr, and recitation of the Quran' (narrated by Muslim). Another evidence is the Hadith of Zayd ibn Arqam, indicating that they were forbidden from speech after the revelation of Quran 2:238, and the Hadith of Ibn Mas'ud where the Prophet informed them after returning from Abyssinia that Allah had ordained that no speech should occur in prayer.