Burial were Ceremonially Unclean
Source: TTT
Numbers 19:16, 18
Anyone in the open field who touches someone who has been killed by the sword or has died of natural causes, or anyone who touches a human bone or a grave, will be unclean for seven days. / Then a man who is ceremonially clean is to take some hyssop, dip it in the water, and sprinkle the tent, all the furnishings, and the people who were there. He is also to sprinkle the one who touched a bone, a grave, or a person who has died or been slain.