The Prophet ﷺ said, "A single suckling or two sucklings do not establish the prohibition of foster relationship."
قال حدثنا يحيى بن سعيد عن هشام قال أخبرني أبي
أن النبي ﷺ قال لا تحرم من الرضاع المصة والمصتان
Its isnad is sahih. Hisham is Ibn Urwa bin Abdullah bin Zubayr, a well-known imam. The hadith was narrated by Muslim, 2/1073, no. 1450, in the chapter on breastfeeding, one suckle or two suckles, and Abu Dawud, 2/224, no. 2063, and Tirmidhi, 3/446, no. 1150, and Nasai, 6/101, no. 3309, and Ibn Majah, 1/624, no. 1941, and Darimi, 2/208, no. 2251.