Hadith: The Prophet (may Allah's peace and blessings be upon him) stayed in Makkah for ten years and then in Madīnah for ten years, and the Qur’an was descending upon him (in both)

عن عائشة وابن عباس رضي الله عنهم : «أنَّ النبيَّ صلى الله عليه وسلم لَبِثَ بمكَّة عشرَ سِنِين، يَنْزلُ عليه القرآنَ، وبالمدينة عشرًا».
[صحيح] - [رواه البخاري]

‘Ā’ishah and Ibn ‘Abbās (may Allah be pleased with both of them) reported that the Prophet (may Allah's peace and blessings be upon him) stayed in Makkah for ten years and then in Madīnah for ten years, and the Qur’an was descending upon him (in both).
Sahih/Authentic. - [Al-Bukhari]

Explanation

This Hadīth shows that the Prophet (may Allah's peace and blessings be upon him) stayed for ten years in Makkah, after having become a Prophet, and stayed for ten years in Madīnah as well, and that the Qur’an was sent down on him during that whole period. It is proved in other than this Hadīth that the Prophet (may Allah's peace and blessings be upon him) stayed in Makkah for thirteen years after he had been sent as a Prophet. Both traditions could be reconciled as follows: the Prophet (may Allah's peace and blessings be upon him) stayed for three years in Makkah without proclaiming his message. After that, the revelation was sent down successively. It is as if those who reported the ten-year-period did not count those three years, or they just rounded up the thirteen years to ten.