It is narrated from al-Sha'bi that Sayyiduna Abu Bakr (may Allah be pleased with him) was asked about kalalah, and he said: I will give my own opinion; if it is correct, it is from Allah, and if it is wrong, it is from me and from Satan. In my view kalalah is one who has neither children nor parents. When Sayyiduna Umar (may Allah be pleased with him) was made caliph, he said: I feel shy before Allah to reject something that Abu Bakr (may Allah be pleased with him) said.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12263