Reference for Eruvin 102:7
רבי יהודה אומר אחד עני ואחד עשיר מערבין ברגל ויצא עשיר חוץ לתחום ויאמר תהא שביתתי במקומי וזה הוא עיקרו של עירוב והתירו חכמים לבעל הבית לשלח עירובו ביד עבדו ביד בנו ביד שלוחו בשביל להקל עליו
A rich man, furthermore, must not proceed beyond the Sabbath limit<span class="x" onmousemove="('comment',' Sc. within four cubits from that limit. Beyond that distance no 'erub can be effective at all.');"><sup>23</sup></span> and make the declaration, 'Let my Sabbath base be where I stand now because it is only for the benefit of one who was under way when it became dusk<span class="x" onmousemove="('comment',' In consequence of which he is unable to obtain bread.');"><sup>24</sup></span> that the Rabbis have enacted that an 'erub may be prepared with one's feet; so R'Meir.<span class="x" onmousemove="('comment',' Which shows, in agreement with R. Nahman, that, according to R. Meir, even where a person is on the very spot which he appointed as his Sabbath base, an 'erub without bread is permitted to him only if he is poor.');"><sup>25</sup></span> R'Judah ruled: Both poor and rich must prepare their 'erub with their feet.