Hadith 8:261
Mirqat
380 says that Tirmidhi is the source in which this tradition is found. I have looked for it with the help of the Concordance, but have been unable to find it.
وَعَنْ عَائِشَةَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «تَهَادُوا فَإِنَّ الْهَدِيَّةَ تُذْهِبُ الضَّغَائِنَ» . رَوَاهُ
Original Reference: Mishkat al-Masabih 3027