Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
suyuti:1758a –
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السيوطي:١٧٥٨a –

"إِذا دَخَلَ أَحَدُكُمْ المسْجِدَ فَليَقُلْ: صَلى اللهُ على محمد، اللهُم افتح لي أَبْوَابَ رَحْمَتِكَ وَأغْلِقْ عنِّي أبْوَابَ سَخَطِكَ، واصرف عنِّي الشيطانَ ووسْوسَتَه".  

الديلمى عن ابن عمر

See similar narrations below:

Collected by Suyūṭī
suyuti:1746a –

"The Messenger of Allah said: 'When anyone of you enters the mosque, let him send peace upon the prophet, then let him say: "Allahummaftah li abwaba rahmatika (O Allah, open to me the gates of Your mercy)." And when he leaves, let him say: "Allahumma inni as'aluka min fadlika. (O Allah, I ask of you from Your bounty)." (Using translation from Ibn Mājah 772)   

السيوطي:١٧٤٦a –

"إِذا دخلَ أحدُكم المسجِدَ فَليُسَلمْ، ثُمَّ ليَقُلْ: اللهمّ افْتَحْ لي أبْوَابَ رَحْمَتِكَ، وإذا خرجَ فَليُسَلِّمْ على النبيِّ، وليقُلْ: اللهمَّ اعْصِمني من الشيطانِ".  

[هـ] ابن ماجة [حب] ابن حبّان وابن السنى، [ك] الحاكم في المستدرك [ق] البيهقى في السنن عن أبي هريرة