Bārakallāhu lak, wa bāraka `alayk, wa jama`a baynakumā fī khayr. May Allah bless you, and shower His blessings upon you, and join you together in goodness. Reference: Abu Dawud, Ibn Majah and At-Tirmidhi. See also Al-Albani, Sahih At-Tirmidhi 1/316.