Where in the Bible might I find that it is sinful to do genealogy on our family?

Answer:

There are two texts in the Scriptures which pertain to genealogies.

“…command certain persons to give up teaching erroneous doctrines and studying those interminable myths and genealogies, which issue in mere speculation and cannot make known God’s plan for us.” (1 Tim 1:3-4 NEB)

“…avoid foolish disputes, genealogies, contentions, and strivings about the law; for they are unprofitable and useless” (Titus 3:9)

The Apostle Paul places genealogies in a class of useless activities that create strife and do not profitably instruct. Searching out one’s genealogy is time consuming, and is of little profit. What practical benefit can there be? If our first interest is to prepare to live in God’s future Kingdom, we will find far more profitable occupation for our time than tracing our ancestors.

During the time when God had a people on earth with whom He was working, and one’s qualifications for service were determined by one’s family and ancestry, tracing genealogy was profitable and necessary (Neh. 7:64). Again, when they were commanded not to intermarry with foreign people to avoid being contaminated by their pagan practices, a record of genealogy was important (Ezra 10).