Abdul-Rahman bin Abu Layla reported,
I was with Umar 
when a man came to him and said, "I have seen the crescent moon of Shawwal."Umar announced, "People, break your fast."Then he stood up, went to a large bowl of water, performed ablution, and wiped over his leather socks.The man said, "By Allah, Commander of the Believers, I came to you only to ask about this very matter. Have you seen anyone else do it?"Umar replied, "Yes, someone better than me and better than the entire ummah. I saw Abu Qasim ﷺ do exactly what I did. He was wearing a Syrian robe with narrow sleeves, so he slipped his hand out from underneath the robe."Then Umar prayed Maghrib.
Ahmad 193
Daifحدثنا يزيد أنبأنا إسرائيل بن يونس عن عبد الأعلى الثعلبي
عن عبد الرحمن بن أبي ليلى قال
كنت مع عمر رضي الله عنه فأتاه رجل فقال إني رأيت الهلال هلال شوال فقال عمر رضي الله عنه يا أيها الناس أفطروا ثم قام إلى عس فيه ماء فتوضأ ومسح على خفيه فقال الرجل والله يا أمير المؤمنين ما أتيتك إلا لأسألك عن هذا أفرأيت غيرك فعله فقال نعم خيرا مني وخير الأمة رأيت أبا القاسم ﷺ فعل مثل الذي فعلت وعليه جبة شامية ضيقة الكمين فأدخل يده من تحت الجبة ثم صلى عمر المغرب
No references are available.
Its chain is daif due to a break in transmission, for Abdul-Rahman bin Abu Layla was very young during the lifetime of Umar, having been born six nights before the end of his caliphate, as he himself stated in what Khatib reported from him in Tarikh Baghdad 10/300, and as is also mentioned in Tahdhib.As for his statement here, "I was with Umar," and so on, in our view this is an error on the part of Abdul-Ala bin Amir Thalabi, who is truthful but prone to mistakes. Ahmad, Abu Zura, and others declared him daif. The Hafiz said in Tahdhib, "Tabari graded his hadith about the eclipse sahih, Tirmidhi graded it hasan, and Hakim graded it sahih," which reflects Hakim's leniency.The hadith will come again at number 307 by the same route, also from Ibn Abu Layla, who said, "I was with Bara bin Azib and Umar bin Khattab." Ibn Saad related it in Tabaqat 6/75 from Malik bin Ismail, from Israil, from Abdul-Ala, so the entire hadith revolves around Abdul-Ala.Ibn Hazm related it in Muhalla 6/238 by the route of Muhammad bin Jafar, from Shuba, from Ali bin Abdul-Ala, from his father, from Abdul-Rahman bin Abu Layla, from Bara, and Ibn Hazm graded it sahih. This version has a connected chain.So either the hadith is from Ibn Abu Layla, from Bara, or Ibn Abu Layla witnessed this from Umar while he was very young, with Bara present, and then when Bara later narrated it, he mentioned it. Though this latter possibility is far-fetched and strange. Allah knows best.See also 87, 88, 128.