Abdullah bin Masud reported,

While we were with the Messenger of Allah ﷺ on one of his journeys, we heard someone calling out, "Allah is the greatest, Allah is the greatest."The Prophet of Allah ﷺ said, "He is upon the natural disposition."Then the man said, "I bear witness that there is no god but Allah."The Prophet of Allah ﷺ said, "He has been delivered from the Fire."We hurried toward him and found that he was a herdsman whom the time of prayer had overtaken, so he had given the call to prayer.

Azami 1887

Sahih

عن عبد الله بن مسعود قال

بينما نحن مع رسول الله ﷺ في بعض أسفاره سمعنا مناديا ينادي: الله أكبر الله أكبر فقال نبي الله ﷺ: على الفطرة فقال: أشهد أن لا إله إلا الله، فقال نبي الله ﷺ: خرج من النار فابتدرناه، فإذا هو صاحب ماشية أدركته الصلاة فنادى بها.

الأعظمي 1887صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Prayer
Chapter
Adhan
Section
Recommendation of adhan for one who prays alone
Numbering
Jami al-Kamil 1887 (2nd edition)
Azami 1887