Reference for Kiddushin 4:11

אִשָּׁה נָשָׂאתִי בִּמְדִינַת הַיָּם, הֲרֵי הִיא זוֹ וְאֵלּוּ בָנֶיהָ, מֵבִיא רְאָיָה עַל הָאִשָּׁה וְאֵין צָרִיךְ לְהָבִיא רְאָיָה עַל הַבָּנִים. מֵתָה, וְאֵלּוּ בָנֶיהָ, צָרִיךְ לְהָבִיא רְאָיָה עַל הָאִשָּׁה וְעַל הַבָּנִים:

(If he said:) "I married a woman abroad, and this is she, and these are her children," he brings proof for the woman, and he need not bring proof for the children. (If he said:) "She died, and these are her children," he must bring proof for the woman and for the children.

Jastrow