Abdullah bin Ubayd reported,
A man said, "Abu Abdul-Rahman, I see that you only touch these two corners."He replied, "I heard the Messenger of Allah ﷺ say, 'Touching them wipes away sins,' and I heard him say, 'Whoever circumambulates seven times, it is equivalent to freeing a slave.'"
Nasai 2922
Hasanحدثنا أبو عبد الرحمن أحمد بن شعيب من لفظه قال أنبأنا قتيبة قال حدثنا حماد عن عطاء
عن عبد الله بن عبيد بن عمير
أن رجلا قال يا أبا عبد الرحمن ما أراك تستلم إلا هذين الركنين قال إني سمعت رسول الله ﷺ يقول إن مسحهما يحطان الخطيئة وسمعته يقول من طاف سبعا فهو كعدل رقبة
[Its isnad is hasan]. It is in Kubra, hadith 3951. Hammad is Ibn Zayd, Ata is Ibn Saaib, and Abu Abdul-Rahman is Abdullah bin Umar bin Khattab 
. Tirmidhi narrated it, hadith 959, from the hadith of Ata bin Saaib, from Ubayd bin Umayr, from his father, etc, and Hakim graded it sahih in 1/489, and Dhahabi agreed, via the route of Jareer, from Ata, with the same wording. The route of Tirmidhi is preferred, and Allah knows best.