In Islam, a Muslim is encouraged to look after and take care of children who have no parents and to treat them justly. To ill-treat them or to treat them unjustly is one of the worst kinds of oppression that is totally prohibited in Islam.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: The sin of maltreating orphans is so enormous and grave, its consequences are beyond what one could imagine if one has even scant faith in accountability before Allah on the Day of Judgment, a day when all our deeds, both major and minor, outward and inward, will be presented for scrutiny and judgment.

Mistreatment or abuse of orphans is undoubtedly one of the gravest sins in the Qur’an. Let me explain:
1. Allah orders us to excel in rendering honorable treatment towards orphans; therefore, any failure or complacency on our part in this regard is reckoned as a most heinous offence and sin: Allah says, (Nay, you do not treat the orphan honorably and generously!) (Al-Fajr 89: 17). In other words, by such an action we stand to incur Allah’s wrath. Elsewhere in the Qur’an, Allah explicitly warns us against inflicting any kind of harm or abuse on an orphan: (As for the orphan do not oppre
ss him (rather, pay him his due of kindness and loving care).) (Ad-Duha 93: 9).
2. Once someone complained to the Prophet (peace and blessings be upon him) that he often experienced hardness in his heart; the Prophet (peace and blessings be upon him) told that the remedy was to act kindly and gently towards orphans. He also said, “The best house is the one where orphans are cared for and treated most honorably and kindly.” By the same logic, the worst house is the one where orphans are abused or mistreated. He further warned those who abuse orphans, “O Allah! You be the witness that I consider any violation of the rights of orphan and woman as an enormity entailing serious consequences!” He also gave glad tidings to those who excel in their kindness towards the orphans, “I and the one who cares for the orphans excellently will be as close in Paradise as these two fingers of mine!”
3. When the Prophet saw one of his Companions who was new to Islam treating his servant roughly, the Prophet said, “They are your brothers whom Allah has entrusted you to your care; so be careful how you treat them. Remember, Allah has power over both of you!” What would the Prophet have told your friend who is abusing a helpless orphan! I cannot even imagine what would be his reaction!
4. The foremost sin in the Qur’an and the Sunnah, second only to shirk (associating partners with Allah), is zhulm (oppression, injustice). The Qur’an and the Sunnah are replete with texts that describe zhulm in all forms as the most abominable of all sins, entailing swift punishment from Allah. There is, however, no form of zhulm that can top the abuse of orphans,
since they are the most helpless and vulnerable. Allah says, (And for the unjust there is no helper (who shall save them against the wrath and punishment of Allah).” (Al-Hajj: 71); also, “(O Prophet) warn them of the near day when hearts will leap up to the throats and choke them; when the unjust will have no friend, nor any intercessor who will be listened to.) (Ghafir 40: 18)
5. Finally, your friend may do well by reflecting on the following authentic hadith:
“The Prophet (peace and blessings be upon him) once asked (his Companions): “Do you know the bankrupt person?” He repeated the question three times; the Companions replied, “The bankrupt person among us is the one who has no money.” The Prophet (peace and blessings be upon him) then said, “But the bankrupt person of my community is one who appears on the Day of Resurrection with lots of prayers, fasts and charities, but he has abused someone, slandered another, devoured someone’s wealth (unlawfully), shed another’s blood, and has beaten still another; so Allah will take rewards of his good deeds and give them to those who had been victimized by him; if all of his good deeds were exhausted before their dues were paid, their sins will be taken and imposed on him, and consequently, he will be thrown into the fire-pit!” (Reported by Muslim).