Audio by Dr. Michael Sokolow

[If one has] two [separate] kabs [of dough] from one of which Hallah had been taken separately, and from the other [too,] separately, and he went back [to them] and made [of] them one dough, R. Akiba declares it exempt, but the Sages declare it liable. [Thus] it is found that [the very proposition giving rise to] the stringency of the one [ruling] is [the proposition that gives rise to] the leniency of the other [ruling]. מ חלה 4.5
שני קבים שניטלה חלתן של זה בפני עצמו ושל זה בפני עצמו, וחזר ועשאן עיסה אחת-- רבי עקיבה פוטר, וחכמים מחייבין; נמצא חומרו קולו
A man may take the requisite amount for Hallah out of a [clean] dough from which Hallah has not [previously] been taken [his purpose being] to effect it in cleanness by way of going on separating [Hallah] therefrom in respect of [unclean] Demai, until it putrifies, since Hallah in respect of Demai may be taken from clean [dough] in respect of unclean [dough], and from [one dough in respect of another dough] which is not close together.  מ חלה 4.6
נוטל אדם כדי חלה מעיסה שלא הורמה חלתה, לעשותה בטהרה, להיות מפריש עליה והולך חלת דמאי, עד שתסרח  שחלת דמאי ניטלת מן הטהור על הטמא, ושלא מן המוקף

Click here for the hebrew/english of Perek 4 from emishna.com