Fadalah bin 'Ubaid (May Allah be pleased with him) reported:
When Messenger of Allah ﷺ led Salat, some people would fall down from their standing posture out of extreme hunger. They were of the people of As-Suffah. The nomad Arabs would say that they were insane. After concluding Salat, Messenger of Allah ﷺ would turn to them and say, "If you were to know what is in store for you with Allah, the Exalted, you would wish to augment your starvation and lack of provisions."

[At-Tirmidhi].

وعن فضالة بن عبيد رضي الله عنه، أن رسول الله ﷺ كان إذا صلى بالناس، يخر رجال من قامتهم في الصلاة من الخصاصة -وهم أصحاب الصفة- حتى يقول الأعراب: هؤلاء مجانين، فإذا صلى رسول الله ﷺ انصرف إليهم، فقال: "لو تعلمون ما لكم عند الله تعالى، لأحببتم أن تزدادوا فاقة وحاجة" ((رواه الترمذي، وقال: حديث صحيح)).
"الخصاصة": الفاقة والجوع الشديد.