Hadith: Verily, I know that you are a stone that can neither harm nor benefit. Had I not seen the Prophet (may Allah's peace and blessings be upon him) kissing you, I would not have kissed you

عَنْ عُمَرَ رَضِيَ اللَّهُ عَنْهُ:
أَنَّهُ جَاءَ إِلَى الحَجَرِ الأَسْوَدِ فَقَبَّلَهُ، فَقَالَ: إِنِّي أَعْلَمُ أَنَّكَ حَجَرٌ، لاَ تَضُرُّ وَلاَ تَنْفَعُ، وَلَوْلاَ أَنِّي رَأَيْتُ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ يُقَبِّلُكَ مَا قَبَّلْتُكَ.
[صحيح] - [متفق عليه] - [صحيح البخاري: 1597]

‘Umar (may Allah be pleased with him) reported:
He came to the Black Stone and kissed it and said: Verily, I know that you are a stone that can neither harm nor benefit. Had I not seen the Prophet (may Allah's peace and blessings be upon him) kissing you, I would not have kissed you.
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 1597]

Explanation

‘Umar ibn al-Khattāb, Commander of the Believers, (may Allah be pleased with him) came to the Black Stone in the corner of the Ka‘bah and kissed it. He, then, said: Verily, I know that you are a stone that can neither harm nor benefit. Had I not seen the Prophet (may Allah's peace and blessings be upon him) kissing you, I would not have kissed you.

Benefits from the Hadith

1. The permissibility of kissing the Black Stone for those performing Tawāf (circumambulation) when they pass by it, if it can be done easily.
2. The purpose of kissing the Black Stone is to follow the Messenger of Allah (may Allah's peace and blessings be upon him).
3. An-Nawawi said: It means that it has no power to bring benefit or harm; it is a created stone like other creations that neither harm nor benefit. ‘Umar proclaimed this during the season so that people from various lands would hear it and preserve it from him.
4. Acts of worship are Tawqīfi (determined by divine texts), therefore, nothing thereof is legitimate except what has been prescribed by Allah and His Messenger.
5. If an act of worship is authentically established, it should be practiced even if its wisdom is not known, for one of the intended purposes is people's compliance and obedience in performing it.
6. The prohibition of kissing stones or other objects as an act of worship unless prescribed in the Shariah.