Reference for Shabbat 301:7
דיקא מתניתין כוותיה דשמואל דקתני עשה לו ארון וחפר לו קבר יקבר בו ישראל אלמא מספיקא שרי הכא נמי מספיקא שרי
The deduction of our Mishnah supports Samuel, for it is stated: IF HE [A GENTILE] MADE A COFFIN FOR HIMSELF OR DUG A GRAVE FOR HIMSELF, AN ISRAELITE MAY BE BURIED THEREIN. This proves that it is permitted on account of a doubt;<span class="x" onmousemove="('comment',' For he might actually have made it for a Jew. [Tosaf. a.l. deletes this passage as in this Mishnah the question of doubt does not arise as explained in the Gemara infra.] ');"><sup>13</sup></span> so here too, it is permitted on account of a doubt. And we learnt in accordance with Rab [too]: A city inhabited by Israelites and Gentiles which contains baths where there is bathing on the Sabbath, if the majority are Gentiles, one [an Israelite] may bathe therein immediately; if the majority are Israelites, one must wait until hot water could be heated;<span class="x" onmousemove="('comment',' V. supra 122a, for notes. ');"><sup>14</sup></span>