Musannaf Ibn Abi Shayba 26:188

Ibn ‘Ulayyah narrated to us, from Abu al-‘Ala’, from Ibrahim, from ‘Alqamah, who said: ‘Abdullah used to make the grandfather a partner with the brothers, and if they were many, he would give him a third. When ‘Alqamah died, I came to ‘Ubaydah, and he told me that Ibn Mas‘ud used to make the grandfather a partner with the brothers, and if they were many, he would give him a sixth. I returned from him feeling distressed. I passed by ‘Ubayd ibn Nadlah, and he said, "Why do I see you distressed?" I said, "How could I not be distressed?" and I told him what happened. He said, "Both of them told you the truth." I said, "May your father be for Allah! How did both of them tell me the truth?" He said, "It was the opinion of ‘Abdullah and his division that he should make him a partner with the brothers, and if they were many, he would give him a sixth. Then he went to ‘Umar and found him making him a partner with the brothers, and if they were many, he would give him a third. So he abandoned his own opinion and followed ‘Umar."