Ibn Lahi'ah informed Ibn Wahb that the Prophet (peace and blessings be upon him) used to say seven and five takbirs in (Eid al-)Fitr and (Eid al-)Adha, besides the takbir of ruku' (bowing).
Muhammad bin Yahya said: This is the mahfuz (preserved) version, because Ibn Wahb heard from Ibn Lahi'ah early on.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة العيدين / 6175