Assalaam alaykum. During a discussion with a Christian, I referred to the hadith of the Prophet, sallallaahu 'alayhi wa sallam, that mentions that smiling to your brother is charity. The thing is is that I changed the word 'brother' to 'someone', so I said, "Smiling to someone is charity." My question is: does this constitute lying about the prophet? If so, then what is required of me because I am aware that the Prophet said that whoever tells a lie on him, then let him take his seat in Hell.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

The authentic version of the hadeeth reads, "Your smiling in the face of your brother is charity..." [At-Tirmithi and others - Al-Albaani graded it saheeh (sound)]

The statement that you mentioned, "Your smiling in the face of someone is charity," is not a hadeeth as far as we know. If you mistakenly changed it and did not deliberately lie about a hadeeth attributable to the Prophet then you bear no sin for that. The Prophet said, "Verily, Allaah, The Exalted, has pardoned for me my community: their mistakes, their forgetfulness, and that which they are forced to do under duress." [Ibn Maajah - Al-Albaani graded it saheeh]

The relevant warning applies only to deliberately attributing a lie to the Prophet as evidenced by the hadeeth that reads, "Whoever deliberately tells lies about me, let him take his place in Hellfire."

Allaah knows best.