Walaikum assalam wa rahmatullah,
Any of the Prophetic supplications related to healing are good. These include:
1. Saying Allahumma ’shfi [name of person]. (“O Allah, heal….”) [Related by Bukhari and Muslim]
2. Saying:
اللَّهُمَّ رَبَّ النَّاسِ مُذْهِبَ الْبَاسِ اشْفِ أَنْتَ الشَّافِي لَا شَافِيَ إِلَّا أَنْتَ شِفَاءً لَا يُغَادِرُ سَقَمًا
Allahumma Rabba n-nas mudhhiba l-bas
Ishfi, anta sh-shafi
La Shafia illa ant
Shifa’an la yughadiru saqama
“O Allah, lord of humanity and remover of harms,
Heal--for You are the healer,
There is no healer but you--
A healing that leaves no sickness.”
[Related by Bukhari, Tirmidhi, Abu Dawud, and others]