Shemos 4 (10) - The possuk says that Moshe turns down the leadership position because of his speech impediment. Rashi says:
“All this [reluctance] was because he [Moses] did not want to accept a position higher than his brother Aaron, who was his senior and was a prophet...”
This means that Moshe's real reason for not accepting the leadership was out of respect to Aharon. If so, why did not Moshe tell this reason to Hashem?