peace, tranquillity, and contentment of the heart for the Holy Prophet صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم, as well as being the confidant of the special matters of the Holy Prophet صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم, because Allah عَزَّوَجَلَّ has said:

وَ جَعَلْنَا  الَّیْلَ  لِبَاسًا﴿ۙ۱۰﴾

And we have made the night a covering.

[Kanz-ul-Īmān (Translation of Quran)] (Part 30, Sūraĥ Nabā, Verse 10)

And Allah عَزَّوَجَلَّ has said:

جَعَلَ لَکُمُ الَّیْلَ وَ النَّہَارَ
 لِتَسْکُنُوْا فِیۡہِ وَ لِتَبْتَغُوْا مِنْ فَضْلِہٖ وَلَعَلَّکُمْ تَشْکُرُوْنَ﴿۷۳﴾

He has made for you the night and the day that you may rest in the night and you may seek His bounty in the day and for this that you may accept the truth.

[Kanz-ul-Īmān (Translation of Quran)] (Part 20, Sūraĥ Al-Qaṣaṣ, Verse 73)

This is an indication towards the system of Dīn being established on the basis of both of these personalities (the Holy Prophet   صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم and Sayyidunā Abū Bakr رَضِىَ اللهُ تَعَالٰی عَنْهُ) in the same way that the system of world is established on the basis of day and night. So if there is no day, nothing will be able to be seen, while if there is no night, there will be no rest or tranquillity. (Mākhūż-az Fatāwā Razawiyyaĥ, Vol. 28, pp. 679-681)