The principle of conservation of electric charge says the algebraic sum of charges before and after a transfer process must be the same. So, we can say that the electric charge it cannot be created or destroyed, only transferred between bodies.
Imagine the process of friction electrification. Initially the bodies to be rubbed are neutral, that is, they have the same number of electrons and protons. After friction, one of the bodies gives up electrons and becomes positively electrified. The other receives the electrons, becoming negatively electrified. By conserving the electric charge, we can say that the number of excess electrons in one body is exactly equal to the number of excess protons in the other. There was only a transfer of electrical charge.
The same observation can be made regarding the processes of contact electrification and induction.
Example
The formation of tritium from the process of Nuclear fusion evidences the conservation of the electrical charge. The formation of tritium occurs with the Fusion of two deuterium nuclei (2H).
2H+ 2H → 3H+p
Tritium is composed of a proton and two neutrons. Note that the electrical charge before and after the fusion is exactly the same, that is, no charge was destroyed or created.
Before the merger: Number of protons = 2 (one for each deuterium)
After the merger: Number of protons = 2 (tritium is formed by 1 proton and two neutrons. Note that 1 proton was released in the reaction.)
Source: Brazil School - https://brasilescola.uol.com.br/fisica/conservacao-carga-eletrica.htm