May Allah the Most High bless…

The one congratulated should reply, saying:

بَارَكَ اللّٰهُ لَكَ وَبَارَكَ عَلَيْكَ وَجَزَاكَ اللّٰهُ خَيْرًا وَّرَزَقَكَ اللّٰهُ مِثْلَهٗ وَاَجْزَلَ ثَوَابَكَ

May Allah the Most High bless you and bestow blessings upon you, may Allah reward you with good, may Allah grant you the like of it, and may He make your reward abundant.

1. This is Imam an-Nawawi's (RH) own saying; see: al-Adhkar of Imam an-Nawawi (1/363).