Whomever Allah has given food, should say: Allāhumma bārik lanā fīhi, wa aṭ`imnā khayran minh. Whomever Allah has given milk to drink, should say : Allāhumma bārik lanā fīhi, wa zidnā minh. Whomever Allah has given food, should say: O Allah, bless us in it and provide us with better than it. Whomever Allah has given milk to drink, should say : O Allah, bless us in it and give us more of it. Reference: At-Tirmidhi 5/506. See also Al-Albani, Sahih At-Tirmidhi 3/158.

مَنْ أَطْعَمَهُ اللَّهُ الطَّعَامَ فَلْيَقُلْ: "اللَّهُمَّ بَارِكْ لَنَا فِيهِ وَأَطْعِمْنَا خَيْراً مِنْهُ"، وَمَنْ سَقَاهُ اللَّهُ لَبَناً فَلْيَقُلْ "اللَّهُمَّ بَارِكْ لَنَا فِيهِ وَزِدْنَا مِنْهُ"