´It was narrated that Al-Hasan said:` "Aqil bin Abi Talib married a woman from Banu Jusham, and it was said to him: 'May you live in harmony and have many sons.' He said: 'Say what the Messenger of Allah said: Barak Allahu fikum, wa baraka lakum. (May Allah bless you and bestow blessings upon you.)'"
Explanation & Benefits
Hafiz Muhammad Ameen
The first method of congratulation was a custom from the Age of Ignorance (Jahiliyyah), therefore it was changed. In any case, the name of Allah Ta'ala must necessarily be mentioned in supplication (du'a). The distinction between a believer (mu'min) and a disbeliever (kafir) is made precisely through the mention of Allah Ta'ala's name.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3373