What is the ruling on greeting a person by saying “May Paradise welcome you”?
Question

Is it permissible to respond to a person who says “Welcome” by saying “May Paradise welcome you”? Is it valid to say this?
Praise be to Allah.When someone says “welcome” (or “hello”), you should say something similar or better than it, because Allah, may He be exalted, says (interpretation of the meaning): {When you are given a greeting, respond with a better greeting, or [at least] with the like thereof. Verily, Allah takes careful account of all things} [an-Nisa’ 4:86].
The phrase translated from Arabic here may be translated as a statement (“Paradise will welcome you”); this it is a lie and it is not permissible to say it.
But if it is by way of supplication (“May Paradise welcome you”) – which is what appears to be the case – praying that Paradise will welcome him, we do not know that Paradise itself will welcome those who will enter it. Rather the angels will welcome the people of Paradise, as Allah, may He be exalted, says (interpretation of the meaning):
{Those who feared their Lord will be ushered to paradise in groups until, when they reach it, they will find its gates wide open, and its keepers will say to them: Peace be upon you; you have done well, so enter it, to abide herein forever} [az-Zumar 39:73].
And Allah, may He be exalted, says (interpretation of the meaning):
{gardens of perpetual abode, which they will enter together with the righteous among their forebears, their spouses, and their offspring. Angels will enter unto them from every gate [saying]:
Peace be upon you because you patiently persevered. How excellent is the ultimate end!} [ar-Ra‘d 13:23-24]
{The greatest terror will not grieve them; and the angels will welcome them [saying]: This is your day, that you were promised} [al-Anbiya’ 21:103].
Matters of the unseen are tawqeefi [meaning that they are to be based on the religious texts of the Qur’an and saheeh Sunnah, and are not subject to ijtihad], and cannot be spoken of except on the basis of evidence.
As there is no evidence to prove that Paradise will welcome its people, it is better not to say that, because there is the fear that this may be overstepping the mark in supplication.
Abu Dawud (96), Ibn Majah (3894) and Ahmad narrated that ‘Abdullah ibn Mughaffal heard his son saying: O Allah, I ask You for the white palace on the right-hand side of Paradise, if I enter it. He said: O my son, ask Allah for Paradise and seek refuge with Him from Hell, for I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “There will be people in this ummah who will overstep the mark in purification and supplication.” This hadith was classed as sahih by al-Albani in Sahih Abi Dawud.
Therefore you should not say that, and you should use the well-known words of greeting and welcoming people.
And Allah knows best.