Abu Bakr reported: The Messenger of Allah, peace and blessings be upon him, said, “Go out and announce to the people that whoever testifies there is no God but Allah will surely enter Paradise.” I went out and was met by Umar ibn al-Khattab. Umar said, “Return to the Messenger of Allah, for I fear they will take it for granted.” I returned to the Messenger of Allah and he said, “Why have you come back?” I told him what Umar had said, and the Prophet said, “He spoke the truth.”
Source: Musnad Abī Ya’lá 105
Grade: Sahih (authentic) according to Al-Albani
عَنْ أَبِي بَكْرٍ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ اخْرُجْ فَنَادِ فِي النَّاسِ مَنْ شَهِدَ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَجَبَتْ لَهُ الْجَنَّةُ فَخَرَجْتُ فَلَقِيَنِي عُمَرُ بْنُ الْخَطَّابِ فَقَالَ عُمَرُ ارْجِعْ إِلَى رَسُولِ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ فَإِنِّي أَخَافُ أَنْ يَتَّكِلُوا عَلَيْهَا فَرَجَعْتُ إِلَى رَسُولِ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ فَقَالَ مَا رَدَّكَ فَأَخْبَرْتُهُ بِقَوْلِ عُمَرَ فَقَالَ صَدَقَ
105 مسند أبي يعلى
1135 المحدث الألباني خلاصة حكم المحدث إسناده صحيح بنحوه في السلسلة الصحيحة