Is retribution permitted in this era? I would like proof, please.

Allah (SWT) has permitted and legislated retribution (Qisas) for the wronged against the wrongdoer, as stated in the two noble verses: "O you who have believed, prescribed for you is legal retribution for those murdered — the free for the free, the slave for the slave, and the female for the female. But whoever is pardoned by his brother of something, then [pursue it] with fairness and pay [him] with excellence. This is an alleviation from your Lord and a mercy. But whoever transgresses after that will have a painful punishment" and "And do not kill the soul which Allah has forbidden, except by right. And whoever is killed unjustly — We have given his heir authority, but let him not exceed limits in [the matter of] killing. Indeed, he has been supported." However, the implementation of retribution and hudud (punishments ordained by Allah) is solely vested in the ruler or his deputy, as stated by An-Nawawi.