In Parshat Beshalach, at the beginning of רביעי it says that HaShem told Moshe that he should hit the water with his hand. The אור החיים asks why HaShem commands Moshe to hit the water with his hand – and not the stick. If Moshe used the stick for almost all the makot, why doesn’t he use it here? The answer is that HaShem wanted the last Makkah on the Egyptians to be without any materiality, and this is why HaShem told Moshe to hit the water with his hand. Additionally, I would like to share another answer. There is an interesting story of one man who had a small stone. He wondered about its identity and went to ask Moses Mendelson what it was. He didn’t know – but wanted to make fun of the Vilna Gaon. Thus, he asked him to ask the same question to the Gra. He went to meet the Gra, but he also was unsure of its identity. Leaving it in his room, a child went in and saw the stone. He placed it into a bucket of water, which thus caused the water to split into two. Through this, he knew it was the same stone used to split the water when leaving Mitzrayim, called סנפירון. Moses Mendelson asked the Gra – how do we know Moshe didn't use this stone at the end of his staff? He answered that this stone is why Moshe used his hands so that people don't say that he put this stone at the end of his staff in order to split the water
!שבת שלום