It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that he said: "The Messenger of Allah (peace and blessings be upon him) taught Sayyiduna al-Hasan bin Ali (may Allah be pleased with them both) that when he entered the mosque he should send blessings upon the Prophet (peace and blessings be upon him) and say: 'Allahumma ighfir lana dhunubana, waftah lana abwaba rahmatik' (O Allah, forgive us our sins and open for us the doors of Your mercy), and when he went out of the mosque he should send blessings upon the Prophet (peace and blessings be upon him) and say: 'Allahumma iftah lana abwaba fadlik' (O Allah, open for us the doors of Your bounty)."
"No one narrated these two hadiths except Abu al-Fayd (may Allah have mercy on him), and Isma'il bin Subayh (may Allah have mercy on him) is alone in narrating them."
Hadith Referenceالمعجم الأوسط / باب الميم / 6612
Hadith Gradingمحدثین:إسناده ضعيف جدًّا، فيه سالم بن عبد الأعلى متروك
Hadith Takhrij«قال الهيثمي: وفيه سالم بن عبد الأعلى وهو متروك «مجمع الزوائد ومنبع الفوائد، ج 2، ص 32»»