That the Messenger of Allah ﷺ implemented the penalty by beating forty times, with two shoes - Mis'ar (one of the narrators) said: "It think it was for wine."  

أَنَّ رَسُولَ اللَّهِ ﷺ ضَرَبَ الْحَدَّ بِنَعْلَيْنِ أَرْبَعِينَ قَالَ مِسْعَرٌ أَظُنُّهُ فِي الْخَمْرِ قَالَ وَفِي الْبَابِ عَنْ عَلِيٍّ وَعَبْدِ الرَّحْمَنِ بْنِ أَزْهَرَ وَأَبِي هُرَيْرَةَ وَالسَّائِبِ وَابْنِ عَبَّاسٍ وَعُقْبَةَ بْنِ الْحَارِثِ  

That a man who had drunk wine was brought to the Prophet ﷺ, so he beat him about forty times with two stalks of a palm tree. So Abu Bakr did similarly, and by the time 'Umar became Khalifah he sought council from the people. And 'Abdur-Rahman bin 'Awf said: 'I see that the lightest penalty is eighty lashes,' so 'Umar ordered that.  

عَنِ النَّبِيِّ ﷺ أَنَّهُ أُتِيَ بِرَجُلٍ قَدْ شَرِبَ الْخَمْرَ فَضَرَبَهُ بِجَرِيدَتَيْنِ نَحْوَ الأَرْبَعِينَ وَفَعَلَهُ أَبُو بَكْرٍ فَلَمَّا كَانَ عُمَرُ اسْتَشَارَ النَّاسَ فَقَالَ عَبْدُ الرَّحْمَنِ بْنُ عَوْفٍ كَأَخَفِّ الْحُدُودِ ثَمَانِينَ فَأَمَرَ بِهِ عُمَرُ