(a) Arfajah (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) saw a man who was crippled (or chronically ill), and he fell into prostration.
(b) Muhammad bin Ubaydullah narrates that when the good news of a conquest came to Abu Bakr (may Allah be pleased with him) he would prostrate, and when it came to Umar (may Allah be pleased with him) he too would prostrate, or when he saw someone crippled or disabled he would prostrate.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3939