He said, "Messenger of Allah." Yazid said that Tamim asked, "Messenger of Allah, what is the sunnah regarding a man who accepts Islam at the hands of another Muslim?"He replied, "He is the most entitled of people to him in his life and in his death."
حدثنا يزيد بن خالد بن موهب الرملي وهشام بن عمار قالا حدثنا يحيى قال أبو داود وهو ابن حمزة عن عبد العزيز بن عمر قال سمعت عبد الله بن موهب يحدث عمر بن عبد العزيز عن قبيصة بن ذؤيب قال هشام
أنه قال يا رسول الله وقال يزيد إن تميما قال يا رسول الله ما السنة في الرجل يسلم على يدي الرجل من المسلمين قال هو أولى الناس بمحياه ومماته
Its isnad is hasan. Tirmidhi narrated it in the chapter on inheritance, in the section on what has been reported regarding the inheritance of a man who embraces Islam at the hands of another man, hadith 2112, and Ibn Majah, hadith 2752, from the hadith of Abdul-Aziz bin Umar as narrated here. Bukhari mentioned it with a weak formulation of attribution before hadith 6757, and I have not found any strong argument for those who weakened it.