In our region, it is customary to recite a specific supplication during weddings—beginning with the words "Allahumma allif bainahuma..." (O Allah, unite their hearts...). However, this particular supplication was not practiced during the eras of the Prophet (PBUH), the Companions (Sahaba), the Successors (Tabi'in), or the four Imams. It is an innovation introduced by certain individuals from Tamil Nadu.
The supplication is structured to pray that the couple lives like the Prophets and their wives—such as Adam and Hawwa (Eve), or Ayyub (Job) and Rahima.
We do not possess details regarding how those Prophets conducted their marital lives or the extent to which their wives were obedient to them. It is meaningless to pray for a life modeled after theirs without knowing the actual nature of their marital relationships.
The Quran states that one should not follow matters of which one has no knowledge.
(Quran 7:38)
Therefore, such supplications should be avoided. Furthermore, there is no evidence to support the practice of reciting other supplications collectively.
The Prophet (PBUH) offered various supplications for the bride and groom.
When Abdur Rahman bin Awf (RA) informed the Prophet (PBUH) about his marriage, the Prophet said, "Barakallahu laka" (May Allah grant you Barakah—divine, immense blessings beyond sensory perception).
(Bukhari 5155, 6386)
Based on this precedent, one may offer congratulations by saying "Barakallahu laka."
There are also Hadiths indicating that the Prophet (PBUH) taught people to say
"Barakallahu lakum wa baraka 'alaikum." (Ahmad 15181)
When congratulating a newlywed couple, the Prophet (peace be upon him) used to say: "Barakallahu laka wa baraka 'alaika wa jama'a bainakuma fi khair."
Narrator: Abu Hurairah (may Allah be pleased with him)
Source: Tirmidhi 1011, Abu Dawud 1819, Ahmad 8599
The meaning of this is: "May Allah bless you and shower His blessings upon you, and unite the two of you in goodness." Everyone should offer this supplication and congratulation.