Asalamu alaykum wrwb. Sister, tell your friend who asked you this in a kind manner that Allah swt says in the Quran: "On the Day when every soul will be confronted with all the good it has done, and all the evil it has done, it will wish there were a great distance between it and its evil. But Allah cautions you (To remember) Himself. And Allah is full of kindness to those that serve Him."
( سورة آل عمران , Aal-e-Imran, Chapter #3, Verse #30)
At the end of this verse, the words and Allah is full of kindness to those that serve Him stick out. Allah swt is filled with kindness. Allah swt with His kindness would not order and has NOT ORDERED that people cut themselves. Those who do so, are either doing it out of ignorance or out of a ritual from THEIR CULTURE, NOT FROM ISLAM. A person may claim to be a Muslim but that does not mean that they fully practice Islam. They are INDIVIDUALS and THEY CHOOSE FOR THEMSELVES MANY THINGS WHICH ARE NOT FROM ISLAM. Islam is perfect, and Muslims are not. We are humans, we sin and err and that is why we should continously ask for forgiveness. There are deviated sects that claim to be the "right" sect and often they mislead people. So kindly explain to your friend, that this practice is no where mentioned in the Quran or hadiths( it is not from islam). Allah swt tells us not to kill our nafs or souls because we are forbidden to do so.
Allah swt says in the Quran: " And those who, having done something to be ashamed of, or wronged their own souls, earnestly bring Allah to mind, and ask for forgiveness for their sins,- and who can forgive sins except Allah.- and are never obstinate in persisting knowingly in (the wrong) they have done.
( سورة آل عمران , Aal-e-Imran, Chapter #3, Verse #135)
Allah swt also says in the Quran: Whatever good, (O man!) happens to thee, is from Allah. but whatever evil happens to thee, is from thy (own) soul. and We have sent thee as an apostle to (instruct) mankind. And enough is Allah for a witness.
( سورة النساء , An-Nisa, Chapter #4, Verse #79)
and He also again says : Contend not on behalf of such as betray their own souls; for Allah loveth not one given to perfidy and crime:
( سورة النساء , An-Nisa, Chapter #4, Verse #107)
In this above verse Allah swt is telling us not betray our own SOULS. So how then will a person who truly believes in Allah swt cut or kill himself.
Sister i'm still not done searching for solid hadiths and quran verses. i'll write more as soon as i do. and i'm sorry i was not much help to you.