Quotation do Nidda 1:10

A nursing woman whose son dies -- within twenty-four months, she imparts impurity for twenty-four hours. Therefore, if she was nursing him and even five years pass, her time is sufficient, the words of Rabbi Meir. Rabbi Yosei and Rabbi Shimon say, her time is not sufficient; rather, twenty-four months. Therefore, if she was nursing and even four or five years pass, she only has twenty-four months. A nursing woman whose husband dies -- behold, she should not be betrothed or married until twenty-four months [of nursing] pass, the words of Rabbi Meir. Rabbi Yehuda says, eighteen months. Rabbi Yonatan ben Yosef says, Beit Shammai say, twenty-four months, and Beit Hillel say, eighteen months. Said Rabban Shimon ben Gamaliel to the words of the one who says "twenty-four months," it is permitted for her to marry on the twenty-first month, [and] to the words of the one who says "eighteen months," it is permitted for her to marry on the fifteenth month, since milk does not spoil before three months have passed.