as salam alaikum
the opinion of the Ahl al-Bayt and the ijma' of their scholars is that sadl (praying without hands folded) should be performed while standing during salat.
Imami sources establish it through several ahadith on the authority of the Imams of the Ahl al-Bayt like when Imam al-Sadiq describes the modality of salat to Hammad Ibn 'Isa (see "Man la yahduruhu al-Faqih" by Shaykh Saduq, vol. 1, p. 196).
In Zaydi sources there is a hadith on the authority of the Messenger of Allah, peace be upon him and his family, in the "Manahi" of Ibn Mansur where he stops a man while praying with folded hands saying that this is the way of the prayer of Ahl al-Kitab.
In Sunni sources many scholars of the Malikiyyah and some of the Shafi'iyyah brought forth a sahih hadith from Sunan al-Nisa'i as evidence.
Ibadi sources report an hadith on the authority of the Prophet in this regard (see "al-Idah" by 'Amir Ibn 'Ali al-Shamakhi).
As far as the Qur'an, some scholars have quoted the verse "The believers are successful! Those who have khusu' in their prayers" (23:1-2) and said that praying with folded hands would invalidate the khusu' during salat. Wa Allahu A'lam.
With prayers for your success.