I asked Ata, "At what time do you prefer that I pray Isha, whether leading others or alone?"He replied, "I heard Ibn Abbas say, 'The Messenger of Allah ﷺ once delayed the Isha prayer until the people had fallen asleep, woken up, fallen asleep again, and woken up once more. Then Umar bin Khattab stood and called out, "The prayer!"'"Ata continued, Ibn Abbas said, "Then the Prophet of Allah ﷺ came out, and it is as if I can see him now, water dripping from his head, his hand placed on the side of his head. He said, 'Were it not that I would burden my community, I would have ordered them to pray it at this time.'"
حدثنا عبد الرزاق وابن بكر
قال قلت لعطاء أي حين أحب إليك أن أصلي العشاء إماما أو خلوا قال سمعت ابن عباس يقول أعتم رسول الله ﷺ ليلة بالعشاء حتى رقد الناس واستيقظوا ورقدوا واستيقظوا فقام عمر بن الخطاب رضي الله عنه فقال الصلاة قال عطاء قال ابن عباس فخرج نبي الله ﷺ كأني أنظر إليه الآن يقطر رأسه ماء واضع يده على شق رأسه فقال لولا أن أشق على أمتي لأمرتهم أن يصلوها كذلك
Its isnad is sahih. Its meaning has already appeared in brief at 1926, where we noted that Bukhari narrated it at length. This is that lengthy narration."Khalwa" is with a kasrah on the kha and a sukun on the lam, meaning alone.