Mishnayos Rosh Hashanah Perek 1 Mishnah 7

If a father and his son saw the new moon, they should both go to the court in Jerusalem. It is not that they can join together to give testimony, for close relatives are disqualified from testifying together, but they both go so that if one of them is disqualified, the second may join together with another witness to testify about the new moon. Rabbi Shimon says: A father and his son and all their relatives are fit to combine together as witnesses for testimony to determine the start of the month. Rabbi Yosei said: There was an incident with Toviyya the doctor. When he saw the new moon in Jerusalem, he and his son and his freed slave all went to testify. The priests accepted him and his son as witnesses and disqualified his slave, for they ruled stringently that the month may be sanctified only on the basis of the testimony of those of Jewish lineage. And when they came before the court, they accepted him and his slave as witnesses and disqualified his son, due to the familial relationship.

אָב וּבְנוֹ שֶׁרָאוּ אֶת הַחֹדֶשׁ, יֵלְכוּ. לֹא שֶׁמִּצְטָרְפִין זֶה עִם זֶה, אֶלָּא שֶׁאִם יִפָּסֵל אֶחָד מֵהֶן, יִצְטָרֵף הַשֵּׁנִי עִם אַחֵר. רַבִּי שִׁמְעוֹן אוֹמֵר, אָב וּבְנוֹ וְכָל הַקְּרוֹבִין, כְּשֵׁרִין לְעֵדוּת הַחֹדֶשׁ. אָמַר רַבִּי יוֹסֵי, מַעֲשֶׂה בְטוֹבִיָּה הָרוֹפֵא, שֶׁרָאָה אֶת הַחֹדֶשׁ בִּירוּשָׁלַיִם, הוּא וּבְנוֹ וְעַבְדּוֹ מְשֻׁחְרָר, וְקִבְּלוּ הַכֹּהֲנִים אוֹתוֹ וְאֶת בְּנוֹ, וּפָסְלוּ אֶת עַבְדּוֹ. וּכְשֶׁבָּאוּ לִפְנֵי בֵית דִּין, קִבְּלוּ אוֹתוֹ וְאֶת עַבְדּוֹ, וּפָסְלוּ אֶת בְּנוֹ: