SatNaam,
 
Guru Gobind Singh Ji wrote the following passage in praise of Dhan Guru
Nanak bringing the Great Mantra of SatNaam:-

ਸਤਿਗੁਰੁ
ਨਾਨਕ ਅੰਸ ਕਲਾ ਪ੍ਰਭੁ, ਤਿਨ ਸੁਭ ਗ੍ਰੰਥ ਬਖਾਨੇ ॥
Satguru
Nanak is the true lineage (ans) and power (shakti) of the Lord,


He
recited the pure scripture (granth).

ਨਾਮ ਉਪਾਸਨ, ਨਾਮ ਅਰਾਧਨ, ਨਾਮਹਿ ਜਪੁ ਤ੍ਰਿਪਤਾਨੇ ॥
(In
the scripture it says) Worshiping the Name, Taking support of the Name,


and
reciting the name you shall be carried across (the terrifying ocean
that is the world)

ਸਚੁ ਉਪਦੇਸ ਸੰਗਤਿ ਕਉ ਦੀਨਾ, ਬਸਤੁ ਨਾਮ ਨਿਰਬਾਨੇ ॥
Giving
the teachings of Truth to the Sangat,


the
Naam emancipated them



ਮਹਾਂਮੰਤ੍ਰ ਤਾਰਕ ਸਤਿਨਾਮਾ, ਸੋ ਗੁਰੁ ਕੀਨੋ ਦਾਨੇ ॥੩॥
The
Guru gave the Great Mantra (MahaMantra) of “SatNaam”,


the
one which shall take you across (the ocean that is this world).

From Sarbloh Granth – chapter 5, page 631 (Vol. II of Steek)
 
 
http://sikh-reality.blogspot.com/2009/11/guru-nanak-dev-ji-passage-from-sarbloh.html