Hadithcore
Sahih al-Bukhari, 5069
sahih

Narrated Sa`id bin Jubair:

Ibn `Abbas asked me, "Are you married?" I replied, "No." He said, "Marry, for the best person of this (Muslim) nation (i.e., Muhammad) of all other Muslims, had the largest number of wives."

حَدَّثَنَا عَلِيُّ بْنُ الْحَكَمِ الأَنْصَارِيُّ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ رَقَبَةَ، عَنْ طَلْحَةَ الْيَامِيِّ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، قَالَ قَالَ لِي ابْنُ عَبَّاسٍ هَلْ تَزَوَّجْتَ قُلْتُ لاَ‏.‏ قَالَ فَتَزَوَّجْ فَإِنَّ خَيْرَ هَذِهِ الأُمَّةِ أَكْثَرُهَا نِسَاءً‏.‏

References2 variants
In-Book Reference
Book 67, Hadith 7
USC-MSA web (English) reference
Vol. 7, Book 62, Hadith 7 (deprecated numbering scheme)