It is narrated from Sayyidah Safiyyah bint Abi Ubayd (may Allah be pleased with her) that the Mother of the Believers, Sayyidah Hafsah (may Allah be pleased with her), sent Asim bin Abdullah bin Sa'd to her sister, Sayyidah Fatimah bint Umar (may Allah be pleased with them both), for her to suckle him ten sucklings (that is, ten times) so that he could come in to her. He was small and still nursing. She did so, and he used to come in to her.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15640