Abdur Rahman bin Mu’qil said: Sayyiduna Ibn Abbas (may Allah be pleased with them both) was asked about the grandfather, so he said: Who is the greatest among your fathers (grandfathers)? (And in another narration: When the questioner could not answer,) I said: Adam (is the greatest father). He replied: Have you not heard the saying of Allah Almighty: "O children of Adam"?
Hadith Referenceسنن دارمي / من كتاب الفرائض / 2957
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):رجاله ثقات غير أن عبد الله بن خالد لم يسمع ابن عباس بينهما الضحاك، [مكتبه الشامله نمبر: 2966]
Hadith Takhrijاس اثر کے رجال ثقات ہیں، لیکن عبداللہ بن خالد کا سماع سیدنا ابن عباس رضی اللہ عنہما سے ثابت نہیں۔ دیکھئے: [ابن أبى شيبه 11254] ، [البيهقي 246/6]
Brief Explanation
(Commentary on Ahadith 2948 to 2957)
Their likely intent was that the supreme ancestor, Adam (alayhis salam), should be regarded as the father, because when people are called the children of Adam, then Adam (alayhis salam) is indeed their father. And when the supreme ancestor is considered the father, then the lesser ancestors, i.e., the immediate grandfathers, will also be in the rank of father. And Allah knows best.