that the Prophet used to say, when offering congratulations of the occasion of marriage: “Barak Allahu lakum, wa barak 'alaikum, wa jama'a bainakuma fi khair (May Allah bless you and bestow blessings upon you, and bring you together in harmony).”  

أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا رَفَّأَ قَالَ بَارَكَ اللَّهُ لَكُمْ وَبَارَكَ عَلَيْكُمْ وَجَمَعَ بَيْنَكُمَا فِي خَيْرٍ  

that he married a woman from Banu Jusham, and they said: “May you live in harmony and have many sons.” He said: “Do not say that, rather say what the Messenger of Allah said: 'Allahumma barik lahum wa barik ʿalaihim (O Allah, bless them and bestow blessings upon them).' ”  

أَنَّهُ تَزَوَّجَ امْرَأَةً مِنْ بَنِي جُشَمٍ فَقَالُوا بِالرِّفَاءِ وَالْبَنِينَ فَقَالَ لاَ تَقُولُوا هَكَذَا وَلَكِنْ قُولُوا كَمَا قَالَ رَسُولُ اللَّهِ ﷺ اللَّهُمَّ بَارِكْ لَهُمْ وَبَارِكْ عَلَيْهِمْ