Hadith: I used to see the Messenger of Allah (ﷺ) making Taslīm (salutation of peace ending the prayer) to his right and to his left, until I could see the whiteness of his cheek

عَنْ سَعْدٍ رَضِيَ اللَّهُ عَنْهُ قَالَ:
كُنْتُ أَرَى رَسُولَ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ يُسَلِّمُ عَنْ يَمِينِهِ، وَعَنْ يَسَارِهِ، حَتَّى أَرَى بَيَاضَ خَدِّهِ.
[صحيح] - [رواه مسلم] - [صحيح مسلم: 582]

Sa‘d (may Allah be pleased with him) reported:
I used to see the Messenger of Allah (ﷺ) making Taslīm (salutation of peace ending the prayer) to his right and to his left, until I could see the whiteness of his cheek.
[Authentic hadith] - [Narrated by Muslim] - [Sahih Muslim - 582]

Explanation

Sa‘d ibn Abi Waqqās (may Allah be pleased with him) reported that he used to see the whiteness of the Prophet's (ﷺ) cheeks because of how much he would turn his head when making the first Taslīm to his right and the second to his left.

Benefits from the Hadith

1. The permissibility of exaggeration in turning one's head to the right and to the left when making Taslīm.
2. The legitimacy of making two Taslīms—to the right and to the left.
3. An-Nawawi said: If one were to make both Taslīms towards his right side only, or left side only, or directly forward, or even the first to the left and the second to the right, his prayer would still be valid and both Taslīms would be considered complete. However, he would have missed the recommended manner and its associated virtue.