Hadith: No one greets me except that Allah restores my soul to me so that I return his greeting

عَنْ أَبِي هُرَيْرَةَ رضي الله عنه أَنَّ رَسُولَ اللهِ صلَّى الله عليه وسلم قال:
«ما مِنْ أحَدٍ يُسلِّمُ علي إلا ردَّ اللهُ عليَّ رُوحي حتى أردَّ عليه السَّلامَ».
[إسناده حسن] - [رواه أبو داود وأحمد] - [سنن أبي داود: 2041]

Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said:
"No one greets me except that Allah restores my soul to me so that I return his greeting."
[Good chain of narrators] - [Narrated by Abu Daoud & Ahmad] - [Sunan Abu Daoud - 2041]

Explanation

The Prophet (may Allah's peace and blessings be upon him) informs that his soul is restored to him to return the greeting of whoever greets him, whether he is near or far. Life in the Barzakh (the period between death and resurrection) and the grave is a matter of the unseen, and no one knows its reality except Allah, Who is Competent over all things.