Atharvaveda 11.3.45

11.3.45

[4.14]a) tátaś cainam anyā́bhyām aṣṭhīvádbhyāṃ prā́śīr yā́bhyāṃ caitáṃ pū́rva ŕ̥ṣayaḥ prā́śnan |
[4.14]b) srāmó bhaviṣyasī́ty enam āha |
[4.14]c) táṃ vā́ aháṃ nā́rvā́ñcaṃ ná párāñcaṃ ná pratyáñcam |
[4.14]d) tváṣṭur aṣṭhīvádbhyām |
[4.14]e) tā́bhyām enaṃ prā́śiṣaṃ tā́bhyām enam ajīgamam |
[4.14]f) eṣá vā́ odanáḥ sárvāṅgaḥ sárvaparuḥ sárvatanūḥ |
[4.14]g) sárvāṅga evá sárvaparuḥ sárvatanūḥ sáṃ bhavati yá eváṃ véda ||45|| [14]

If thou hast eaten it with other knees (aṣṭhīvánt) than those with which the ancient seers ate this, thou wilt become lame: thus one says to him; it verily [have] I not [eaten] coming hither, nor retiring, nor coming on; with Tvashṭar's knees, therewith have I etc. etc.