You can't find this in Shawnee for a variety of reasons, but the main one being Tecumseh never said it. The poem is a modernization and abbreviation of "The Teachings of Wabasha^†" which appeared in later editions of Ernest Seton's The Gospel of the Redman. While the original edition, published in 1937, included a chapter entitled "The Teachings of Wabasha (Also Ascribed to Tecumseh, Sitting Bull, Crazy Horse, and Wovoka)", it grew with subsequent editions, accumulating material that had appeared in other sections of the book over time. Seton was the founder of the Woodcraft Indians and later one of the founders of the Boy Scouts of America. His influence is largely responsible for the psuedo-Native American elements that have been appropriated into the Scouting movement, and The Gospel of the Redman is prime example of his efforts to appropriate Native wisdom for his own purposes. Very little in the book is accurately sourced. Many quotes are vaguely attributed to nameless ancient prophets or to multiple unrelated people. The alternations made in subsequent editions, reshuffling material under different headings and being attributed to different people, demonstrates that historical rigor was not one of Seton's goals.

The opening line of the 'poem' is, word for word, the opening line of "The Teachings...", but the following line appears as the following, in a separate section entitled "Religion" and attributed to Wabasha and Redjacket:

Trouble no man about his religion - respect him in his view of the Great Spirit, and demand of him that he respect yours. Treat with respect such things as he holds sacred. Do not force your religion on anyone.

The next line, about loving your life, appears in yet another section of the 1937 edition, entitled "The Twelve Commandments" where it is the first half of the twelfth commandment.

We could go on like this for a while, but let's just jump ahead to the end, the last stanza of the poem. In Seton's book it appears as the last part of section entitled "The Indian Creed," immediately before the aforementioned Twelve Commandments:

The soul of man is immortal. Whence it came into this world and whither it goes when it departs , he does not know. But when his time comes to die, he should remember that his going to the next world. What the next life contains for him, he has no means of ascertaining. Nevertheless, he should not approach it with fear or trembling, repenting and weeping over such things as he has left undone, or such things as he should not have done. He should rest assured that he has done his best with the gifts and the limitations that were his, and that his condition there will be governed by his record and his behaviour here. Therefore, let him sing his Death Song, and go out like a hero going home.

In later editions, this was added to "The Teachings of Wabasha" as such:

When your time comes to die, be not like those whose hearts are ever filled with fear of death, so when their time comes, they weep and wail and pray for a little more time to live their lives over again in a different manner. Sing your death song, and die like a hero going home.

The poem makes some slight edits here, but otherwise copies this version of the passage.

†Wabasha would be spelled Wapasha today, or Wáȟpe Šá if we use modern Dakota

Thank you so very much. I'm new to reddit and I'm absolutelty blown away by the extent of your reply. Thank you for taking your time to answer my question, all the best ❤