Narrated Jabir bin 'Abdullah and Salama bin Al-Akwa':

While we were in an army, Allah's Apostle came to us and said, "You have been allowed to do the Mut'a (marriage), so do it." Salama bin Al-Akwa' said: Allah's Apostle's said, "If a man and a woman agree (to marry temporarily), their marriage should last for three nights, and if they like to continue, they can do so;
and if they want to separate, they can do so." I do not know whether that was only for us or for all the people in general. Abu Abdullah (Al-Bukhari) said: 'Ali made it clear that the Prophet ﷺ said, "The Mut'a marriage has been cancelled (made unlawful)."

حَدَّثَنَا عَلِيٌّ، حَدَّثَنَا سُفْيَانُ، قَالَ عَمْرٌو عَنِ الْحَسَنِ بْنِ مُحَمَّدٍ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، وَسَلَمَةَ بْنِ الأَكْوَعِ، قَالاَ كُنَّا فِي جَيْشٍ فَأَتَانَا رَسُولُ اللَّهِ ﷺ فَقَالَ " إِنَّهُ قَدْ أُذِنَ لَكُمْ أَنْ تَسْتَمْتِعُوا فَاسْتَمْتِعُوا ".