What is the ruling on performing a movement that is not part of the prayer, repeatedly and without a valid excuse?

Performing a movement that is not part of the prayer, repeatedly and without a valid excuse—known as ‘amel-i kesîr’—invalidates the prayer according to the Hanafi school. It is difficult to set a precise limit for what constitutes ‘amel-i kesîr’. Some scholars say that performing a non-prayer-related action with both hands, or repeating an action three times consecutively, qualifies. According to another preferred opinion, it is any action that would make an outside observer think the person is not in prayer. Therefore, any behavior during prayer that does not resemble the prescribed acts of prayer and gives the impression that the person is not praying falls under ‘amel-i kesîr’ and invalidates the prayer. A person performing prayer should evaluate their actions and whether they invalidate the prayer according to these explanations. (Ibn Abidin, Reddü’l-muhtâr, 1/605)

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu