Is sending the hands down when rising from rukoo' (bowing) Sunnah, based on the action of Ibn Az-Zubair (may Allah be pleased with him) and the absence of a clear explicit proof contradicting that?

This issue is among the subsidiary matters and recommended acts of prayer, and there has been disagreement about it due to the absence of a clear text. The matter is broad, and Imam Ahmad ibn Hanbal's answer was: "When he raises his head from bowing (ruku'): if he wishes, he may let his hands hang, and if he wishes, he may place his right hand over his left." So, whoever lets their hands hang or clasps them, believing that they are following the Sunnah, will be rewarded, Allah willing.