The OP wanted to be shown FROM HEBREWS that you can lose your salvation:
Hebrews 3:6 “but Christ was faithful as a Son over His house whose house we are IF WE HOLD FAST our confidence and the boast of our hope firm UNTIL THE END.”
Hebrews 3:12 “TAKE CARE, brethren, lest there should be in any one of you an evil, unbelieving heart, in FALLING AWAY from the living God.”
Hebrews 3:13 “But encourage one another day after day, as long as it is till call “Today,” LEST ANY ONE OF YOU be hardened by the deceitfulness of sin.”
Hebrews 3:14 “For we have become partakers of Christ IF WE HOLD FAST the beginning of our assurance firm UNTIL THE END.”
Hebrews 4:1 “Therefore, LET US FEAR lest, while a promise remains of entering His rest, Any one of you should seem to HAVE COME SHORT OF IT.”
Hebrews 4:11 “Let us therefore be diligent to enter that rest, LEST ANYONE FALL through following the same example of disobedience.”
Hebrews 5:9 “and having been made perfect, He became TO ALL THOSE WHO OBEY HIM the source of eternal salvation;”
Hebrews 6:6 (This has been quoted several times by others) “and then have fallen away, I TIS IMPOSSIBLE TO RENEW THEM AGAIN TO REPENTANCE, since they again crucity to themselves the Son fo God and put Him to open shame.”
Hebrews 6:8 “but if it yields thorn and thistles, IT IS WORTHLESS AND CLOSE TO BEING CURSED and it ends up being burned.”
Hebrews 10:36 “For you have NEED OF ENDURANCE so that when youhave done the will of God, you may receive what was promised.”
Hebrews 10:38 “But My righteous one shall live by faith; AND IF HE SHRINKS BACK, My soul has no pleasure in him.”
Hebrews 10:39 “But we are not of those WHO SHRINK BACK TO DESTRUCTION, but of those who have faith to the preserving of the soul.”
Hebrews 11:6 “And without faith IT IS IMPOSSIBLE TO PLEASE HIM, for he who comes to God must believe that He is, and that He is a rewarder of those who seek Him.”
(Here see rest of chapter**–faith is an ACTION VERB**
Noah PREPARED AN ARK
Abraham WENT TO A PLACE, LIVED AS AN ALIEN
Sarah RECEIVED ABILITY TO CONCEIVE
Abraham OFFERED UP ISAAC
Isaac BLESSED JACOB AND ESAU
Jacob BLESSED his sons
Joseph GAVE ORDERS
Moses WAS HIDDEN
Moses REFUSED
Moses LEFT EGYPT etc. to end of chapter
Hebrews 12:1 “…let us also lay aside every encumbrance, and the sin which so easily entangles us, and let us RUN WITH ENDURANCE THE RACE THAT IS SET BEFORE US.”
Hebrews 12:14 “Pursue peace with all men, and the sanctification WITHOUT WHICH NO ONE WILL SEE THE LORD.”
Hebrews 12:15 “See to it that no one COMES SHORT OF THE GRACE OF GOD; that no root of bitterness springing up causes trouble, and by it MANY BE DEFILED.”
Hebrews 12:16 “that there be no immoral or godless person like ESAU, who SOLD HIS OWN BIRTHRIGHT for a single meal.”
Hebrews 12:25 “See to it that you do not refuse Him who is speaking. For if those did not escape when they refused him who warned them on earth, MUCH LESS SHALL WE ESCAPE who turn away from Him who warns from heaven.”