Dua reply when congratulated on a newborn
بَارَكَ اللهُ لَكَ وَبَارَكَ عَلَيْكَ
بَارَكَ اللهُ لَكَ وَبَارَكَ عَلَيْكَ
Barakal-lahu laka wabaraka AAalayk
Translation
May Allah bless you and shower blessings upon you.
When to recite
Said in reply when someone congratulates you on the birth of a child.
Source / Reference
Ibn Sunni