From Sahih Muslim (Hadith 6384):
Abu Huraira reported that 'Umar happened to pass by Hassan as he was reciting verses in the mosque. He (Hadrat 'Umar) looked towards him (meaningfully), whereupon he (gassin) said:I used to recite (verses) when one better than you (the Holy Prophet) had been present (here). He then looked towards Abu Huraira and said to him: I adjure you by Allah (to tell) if you had not heard Allah's Messenger (ﷺ) as saying: (Hassan), give a reply on my behalf; Allah I help him with Ruh-ul-Qudus. He (Abu Huraira) said: By Allah, it is so (i. e. the Prophet actually said these words)
Reference: Muslim 6384