before his sons # 04_NUM_08_13 # And thou shalt set the Levites before Aaron, and before his sons, and offer them [for] an offering unto the LORD. 
before his sons # 04_NUM_08_22 # And after that went the Levites in to do their service in the tabernacle of the congregation before Aaron, and before his sons: as the LORD had commanded Moses concerning the Levites, so did they unto them.