The first occurrence.
Keeping mercy for thousands, forgiving iniquity and transgression and sin, and that will by no means clear the guilty; visiting the iniquity of the fathers upon the children, and upon the children’s children, to the third and to the fourth generation. Exo 34:7
The primitive root.
Strong’s H5341 נצר natsar, a primitive root meaning, “to keep, to watch over.” The 3-letter root is nun + tsadey + resh.
nun נ, ן = the seed, thus continue, heir, son
tsadey צ, ץ = the trail, thus a man concealed, journey, chase, hunt
resh ר = the head of man, thus head, first, top, beginning, man
The story: We ensure the continuation (nun) of a thing when we hunt and acquire (tsadey) its first foundations (resh).