What is the evidence of the Malikis and Shafi'is that the hand does not become impure by touching a dry impurity whose substance cannot be seen, and is this specific to urine only? And is leaving the people or the place of the sin a condition for valid repentance, based on the hadith of the man who killed 99 people?

If the substance of impurity is removed, but its حكم (ruling/effect) remains, and then a pure object that is wet touches the place of impurity, the Malikis and those who agree with them hold that the object that touched it does not become impure. This is because the impurity has been removed, and only its حكم remains, which is an 'ard (an accidental attribute) that does not transfer. However, if a pure object is dry and touches a dry impure object, it does not become impure according to the Malikis, Shafi'is, and others.