Responsa for Shabbat 243:9

מיתיבי אמר להן רבן גמליאל הואיל ושלא בפנינו עשאו נרד בו אימא הואיל ועשאו נרד בו

an Israelite may feed [his cattle therewith] after him, but if [he gathers] on the Israelite's account, it is forbidden. If he draws water to give his cattle to drink, an Israelite may water [his] after him, but if on the Israelite's account, it is forbidden. When is that? If he does not know him; but if he knows him it is forbidden. But that is not so? For R. Huna said in R. Hanina's name: A man may stand his cattle on grass on the Sabbath,<span class="x" onmousemove="('comment',' I.e., on grass attached to the soil, and we do not fear that he may thereby come to cut grass for his animal. ');">¹⁴</span> but not on mukzeh<span class="x" onmousemove="('comment',' Fodder stored away for later use; this may not be handled on the Sabbath as mukzeh (v. Glos.); hence its designation. ');">¹⁵</span>

Teshuvot Maharam