Numbers 19:16 (BSB)

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.

From Numbers 19. Also in the ESV.

Commentary on Numbers 19:16

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Numbers 19:11-22: Directions are here given concerning the use and application of the ashes which were prepared for purification. they were laid up to be laid out; and therefore, though now one place would serve to keep them in, while all Israel lay so closely encamped, yet it is probable that afterwards, when they came to Canaan, some of these ashes were kept in every town, for...
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Numbers 19:16: And whosoever toucheth one that is slain with a sword in the open fields,.... That is killed by another, that dies a violent death, either by the sword or other means; one that touched such an one was unclean, or that touched the sword with which he was slain, as the Targum of Jonathan adds: "or a dead body": that dies a natural death, or...
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on Numbers 19:14-16: Num 19:14-16 Special instructions concerning the defilement. If a man died in a tent, every one who entered it, or who was there at the time, became unclean for seven days. So also did every “open vessel upon which there was not a covering, a string,” i.e., that had not a covering fastened by a string, to prevent the smell of the corpse from penetrating it.