Midrash for Bekhorot 105:33
ליקנינהו לאודנייהו לעובדי כוכבים דלא ליקדש מעיקרא
And whence will you prove that we take into account the possibility of one committing an offence? - For it was taught: We are not permitted to consecrate an animal, nor to make valuation, nor to set aside as devoted<span class="x" onmousemove="('comment',' Dedicated as holy for the priests or sacred use.');"><sup>23</sup></span> nowadays.<span class="x" onmousemove="('comment',' Because we cannot hide them until the Temple is rebuilt and therefore we apprehend that an offence might be committed with them.');"><sup>24</sup></span> But if one did consecrate an animal, or make a valuation or set aside as devoted, the animal is to be destroyed;<span class="x" onmousemove="('comment',' Lit., 'uprooted'.');"><sup>25</sup></span> fruits, garments and vessels shall be allowed to rot and as for money and metal vessels, let him cast them into the Salt Sea. And what is meant by destroying? He locks the door on [the animal] and it dies of itself [from hunger].<span class="x" onmousemove="('comment',' V. A.Z. 13a.');"><sup>26</sup></span> If this be the case,<span class="x" onmousemove="('comment',' That an animal set aside as tithe nowadays is not holy for fear of the law being transgressed.');"><sup>27</sup></span> then a first-born [of an animal] should also not become holy nowadays?<span class="x" onmousemove="('comment',' For fear that it might be shorn etc.');"><sup>28</sup></span> Is then the sanctity of a first-born dependent on us? Is it not hol from the time it leaves the womb? - This is what is meant [by the question]: Let him make over to a heathen the ears of the [mothers of the prospective offspring] so that they shall not be sanctified from the beginning?<span class="x" onmousemove="('comment',' The law being that if a heathen has a share in the first-born it is not subject to redemption, v. supra 2a. If you therefore fear an offence against the law, why not adopt this remedy?');"><sup>29</sup></span>