A man came to the Prophet (sallallaahu alayhi wasallam) and said: ”Admonish me and be brief’”; so the Prophet (sallallaahu alayhi wasallam) said to him:
إِذَا قُمْتَ فِي صَلَاتِكَ فَصَلِّ صَلَاةَ مُوَدِّعٍ
”When you stand for your prayer, then pray a farewell prayer (i.e. as if it is your last Salah before death).”
وَلَا تَكَلَّمْ بِكَلَامٍ تَعْتَذِرُ مِنْهُ غَدًا
”Do not speak with a statement for which you may have to apologize tomorrow.”
وَأَجْمِعِ اليَأسَ مِمَّا فِي يَدَيِ النَّاسِ
”And forgo what is in the hands of the people (i.e. do not be desperate for the worldly possessions of the people).”

Reported by:
[Imaam Ahmad (rahimahullaah) Number: 23498)]
[Imaam Ibn Maajah (rahimahulllaah) Number: 4171]
[Imaam Albaani (rahimahullaah) in As-Saheehah. Number:401]