A hadith-related benefit concerning 'Abd Allah and 'Ubayd Allah, the two sons of 'Umar.

The Shaykh : Look at the precision of hadith science and listen to what is being presented to you and to him. This hadith is narrated in al-Hakim's al-Mustadrak through the route of a man from Madinah named 'Abd Allah ibn 'Umar, whose lineage traces back to 'Umar ibn al-Khattab. He has a brother who is named after him in the diminutive form; his name is 'Abd Allah, and his brother's name is 'Ubayd Allah. Both are sons of 'Umar. The hadith is in Sahih al-Bukhari from 'Ubayd Allah ibn 'Umar without the word of takbir (saying Allahu Akbar). In al-Mustadrak, it is from 'Abd Allah ibn 'Umar with the addition of the word of takbir. What is the difference between the two men? It is like the difference between the sky and the earth. The scholars of hadith agreed to refer to the first as "Abd Allah ibn 'Umar al-Mukabbir" (the elder), and his other brother as "Ubayd Allah ibn 'Umar al-Musagghar" (the younger). The first is weak by the consensus of hadith scholars. Whenever 'Abd Allah ibn 'Umar narrates a hadith, do not let "Abd Allah ibn 'Umar ibn al-Khattab" come to your mind. I told you just now that his lineage traces back to 'Umar ibn al-Khattab, but he is a later figure. So, this 'Abd Allah ibn 'Umar al-Mukabbir from Madinah, if he narrates a hadith, his hadith is weak. His brother 'Ubayd Allah ibn 'Umar al-Musagghar, if he narrates a hadith, his hadith is authentic. Why? Because this one is trustworthy and that one is weak. And that weak narrator's hadith is rejected due to his weakness. What do you think if he contradicts his trustworthy brother? In that case, his hadith becomes munkar (denounced), because the narrator who narrated the word of takbir is weak and contradicted the trustworthy one. So it is said regarding his addition, which is "takbir," that it is a denounced addition. This is what I referred to in some previous answers, that books of fiqh narrate from hadith whatever comes to mind. Therefore, I told you that al-Hafiz al-Zayla'i, the Hanafi, wrote his book Nasb al-Ra'yah li-Ahadith al-Hidayah because the book al-Hidayah contains many hadiths that are not authentic. Al-Zayla'i, may Allah reward him with good, extracted this hadith in this book and named it Nasb al-Ra'yah li-Ahadith al-Hidayah. Likewise, the Shafi'i scholars paid special attention to tracing the hadiths in the books of late Shafi'i jurists. The most extensive and knowledgeable in this field is al-Talkhis al-Habir by al-Hafiz al-'Asqalani. This is regarding the tracing of the hadiths in al-Wajiz. I believe that no woman gave birth to anyone like this al-'Asqalani in the science of hadith after him. So for a hadith like this, you go back there and find it traced, with the defect attributed to 'Abd Allah ibn 'Umar al-Mukabbir from Madinah, and with another defect that his brother 'Ubayd Allah al-Musagghar narrated the hadith without the addition of "takbir," and this narration is in Sahih al-Bukhari. This is the answer to your question, I hope it is clear? Praise be to Allah.