Sayyiduna Abu Umamah al-Bahili (may Allah be pleased with him) narrates from Sayyiduna Abdullah bin Unays al-Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Among the greatest of the major sins are associating partners with Allah, disobedience to parents, and al-yamin al-ghamus (the false oath that plunges a person into sin or into the Fire). And whoever swears an oath by Allah that he has been compelled or bound to take (before a court or ruler) (yamin sabr) and puts into it (a lie) even the size of a mosquito's wing, it will become a black spot on his heart on the Day of Resurrection."
This hadith is not narrated from Abdullah bin Unays (may Allah be pleased with him) except with this chain; Layth (may Allah have mercy on him) is alone in narrating it.
In the printed editions of Dar al-Haramayn and Majma' al-Bahrayn it is recorded in this way (al-Juhani), and the editors of both have explained that the original manuscripts also have this, whereas the correct form is (al-Balawi al-Ansari); and that is indeed so, as is clear from the sources of takhrij. And Allah knows best.
Hadith Referenceالمعجم الأوسط / باب الباء / 3237
Hadith Gradingمحدثین:رجاله موثقون
Hadith Takhrij«قال الهيثمي: رجاله موثقون «مجمع الزوائد ومنبع الفوائد، ج 1، ص 105»» «أخرجه ابن حبان فى «صحيحه» برقم: 5563، والضياء المقدسي فى «الأحاديث المختارة» برقم: 2، 3، 4، 5، والحاكم فى «المستدرك» برقم: 7903، والترمذي فى «جامعه» برقم: 3020، وأحمد فى «مسنده» برقم: 16289، وابن أبي شيبة فى «مصنفه» برقم: 22588، والطحاوي فى «شرح مشكل الآثار» برقم: 893، والطبراني فى «الكبير» برقم: 14932، 14933»