Jami` at-Tirmidhi 3020
جامع الترمذي#3020HasanNarrated Abu Umamah Al-Ansari:from 'Abdullah bin Unais Al-Juhni who said: "The Messenger of Allah (ﷺ) said: 'Indeed among the worst of the major sins is Shirk with Allah, disobeying the parents, the false oath, and none insists on taking an oath in which he swears, including the like of a wing of a mosquito (of falsehood) in it - except that a spot is placed in his heart until the Day of Judgement
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirHasan
Al-AlbaniHasan
Bashar Awad MaaroufHasan
Zubair Ali ZaiIsnaad Hasan
In-book reference: 47:72