Language:
كتاب مناقب الأنصار
63  
Merits of the Helpers in Madinah (Ansaar)
(45)
Chapter: The emigration of the Prophet (saws) to Al-Madina
(45)
باب هِجْرَةُ النَّبِيِّ صلى الله عليه وسلم وَأَصْحَابِهِ إِلَى الْمَدِينَةِ
Sahih al-Bukhari 3907

Narrated Asma:

I prepared the journey food for the Prophet (ﷺ) and Abu Bakr when they wanted (to migrate to) Medina. I said to my father (Abu Bakr), "I do not have anything to tie the container of the journey food with except my waist belt." He said, "Divide it lengthwise into two." I did so, and for this reason I was named 'Dhat-un-Nitaqain' (i.e. the owner of two belts). (Ibn `Abbas said, "Asma', Dhat-un-Nitaq.")

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو أُسَامَةَ، حَدَّثَنَا هِشَامٌ، عَنْ أَبِيهِ، وَفَاطِمَةَ، عَنْ أَسْمَاءَ، رضى الله عنها صَنَعْتُ سُفْرَةً لِلنَّبِيِّ صلى الله عليه وسلم وَأَبِي بَكْرٍ حِينَ أَرَادَا الْمَدِينَةَ، فَقُلْتُ لأَبِي مَا أَجِدُ شَيْئًا أَرْبُطُهُ إِلاَّ نِطَاقِي‏.‏ قَالَ فَشُقِّيهِ‏.‏ فَفَعَلْتُ، فَسُمِّيتُ ذَاتَ النِّطَاقَيْنِ‏.‏
Reference : Sahih al-Bukhari 3907
In-book reference : Book 63, Hadith 132
USC-MSA web (English) reference : Vol. 5, Book 58, Hadith 246
  (deprecated numbering scheme)