I have a question. What is the ruling of saying “Ameen” after reciting al-Fatihah outside of prayer? Is it also a Sunnah as it is in the prayer? Hope for an explanation on this matter.
Alhamdulillah, praise and thanks to Allah for the countless blessings He has blessed us all with. Blessings and salutations to the Prophet Muhammad PBUH, his family, companions and all those that follow his teachings to the day of judgement.
First and foremost, we should know that saying “Ameen” after finishing the recitation of al-Fatihah for each person performing prayer is Sunnah. It is after the phrase: (وَلَا الضَّالِّينَ), which should be followed by the phrase “Ameen”. Likewise, it is also Sunnah to say “Ameen” loudly in each jahriyyah prayers and softly in sirriyah prayers for the imam while the ma’mum says it according to the imam. (See al-Fiqh al-Manhaji, Dar al-Qalam, 1/152). To get further information on this, kindly refer to our article al-Kafi li al-Fatawi Series 540. 
The scholars have differing opinions on the meaning of the phrase “Ameen”. However, the majority of the scholars as cited by Imam Ibn Kathir said that it means (اللَّهُمَّ اسْتَجِبْ لَنَا) which is “O Allah, grant us with it”. (See Tafsir al-Quran al-‘Azim, 1/145 and al-Taqrirat al-Sadidah, pg. 240)
Besides, Imam al-Nawawi also stated that it is Sunnah for the imam to pause a bit (with the shortest pause), between the recitation of al-Fatihah and “Ameen”, so that the public may not think that the phrase “Ameen” is part of the surah. (See al-Tibyan fi Adab Hamalah al-Quran, Dar Ibn Rejab, pg. 93). While Habib Hasan bin Ahmad al-Kaff stated that it is Sunnah for a person performing prayer to pause between the recitation of al-Fatihah and the phrase ‘Ameen’ for the interval of saying ‘Subhanallah’. (See al-Taqrirat al-Sadidah, pg. 238)
Saying “Ameen” after reciting al-Fatihah outside of prayer
Pertaining to the above question, Imam Ibn Kathir stated that:
يُسْتَحَبُّ لِمَنْ قَرَأَ الْفَاتِحَةَ أَنْ يَقُولَ بَعْدَهَا: آمِينَ... قَالَ أَصْحَابُنَا وَغَيْرُهُمْ: وَيُسْتَحَبُّ ذَلِكَ لِمَنْ هُوَ خَارِجُ الصَّلَاةِ، وَيَتَأَكَّدُ فِي حَقِّ الْمُصَلِّي، وَسَوَاءٌ كَانَ مُنْفَرِدًا أَوْ إِمَامًا أَوْ مَأْمُومًا، وَفِي جَمِيعِ الْأَحْوَالِ
“It is Sunnah for those reciting surah al-Fatihah to say afterwards (after finish reciting it): ‘Ameen’… Our ashab (Shafi’ite scholars) and those other than them say that it is also Sunnah for those (who recite it) outside of prayer, in which the right of a person performing prayer is more (is Sunnah), whether he prays alone, he is the imam or the ma’mum. And also in all situations.” (See Tafsir al-Quran al-‘Azim, 1/144-145)
Also, Imam al-Nawawi states that:
يستحب لكل قارئ كان في الصلاة أو في غيرها إذا فرغ من الفاتحة أن يقول أمين
“It is Sunnah for each qari whether it is inside or the opposite (outside of prayer), when he finishes reciting surah al-Fatihah, he should say Ameen which means may Allah grant it”. (See al-Tibyan fi Adab Hamalah al-Quran, Dar Ibn Rejab, pg. 93)
This is in accordance with a hadith narrated by Abu Hurairah RA where the Prophet PBUH said:
إِذَا أَمَّنَ الإِمَامُ فَأَمِّنُوا فَإِنَّهُ مَنْ وَافَقَ تَأْمِينُهُ تَأْمِينَ الْمَلاَئِكَةِ غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ
Say Amin when the Imam says Amin, for it anyone's utterance of Amin synchronises with that of the angels, he will be forgiven his past sins.
Sahih al-Bukhari (780) and Sahih Muslim (410)
In another hadith, it is also narrated from Abu Hurairah RA that the Prophet PBUH said:
إِذَا قَالَ أَحَدُكُمْ آمِينَ . وَالْمَلاَئِكَةُ فِي السَّمَاءِ آمِينَ . فَوَافَقَتْ إِحْدَاهُمَا الأُخْرَى غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ
When anyone amongst you utters Amin and the angels in the heaven also utter Amin and (the Amin) of the one synchronises with (that of) the other, all his previous sins are pardoned.
Sahih al-Bukhari (781) and Sahih Muslim (410)
Based on the above discussion and explanation, we conclude that it is Sunnah to say ‘Ameen’ after finishing surah al-Fatihah whether it is inside or outside of the prayer. Hopefully, we will get the fadhilat and advantages as mentioned in the sahih hadith.
May Allah SWT give us all clear understanding in the religion. Ameen.