The stone is for illegal sexual intercourse
حَدَّثَنَا أَبُو الْوَلِيدِ، حَدَّثَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ قَالَتِ اخْتَصَمَ سَعْدٌ وَابْنُ زَمْعَةَ فَقَالَ النَّبِيُّ صلى الله عليه وسلم " هُوَ لَكَ يَا عَبْدُ بْنَ زَمْعَةَ، الْوَلَدُ لِلْفِرَاشِ، وَاحْتَجِبِي مِنْهُ يَا سَوْدَةُ ". زَادَ لَنَا قُتَيْبَةُ عَنِ اللَّيْثِ " وَلِلْعَاهِرِ الْحَجَرُ ".
Narrated `Aisha: Sa`d bin Abi Waqqas and `Abd bin Zam`a quarrelled with each other (regarding a child). The Prophet (ﷺ) said, "The boy is for you, O `Abd bin Zam`a, for the boy is for (the owner) of the bed. O Sauda ! Screen yourself from the boy." The sub-narrator, Al-Laith added (that the Prophet (ﷺ) also said), "And the stone is for the person who commits an illegal sexual intercourse."