Sheikh Rashîd al-Hasan, professor at King Khâlid University
Supplicating to Allah and mediating towards Him tawassul by way of His names is a lawful practice.
For example, we can say: “O Rahmân, have mercy on me.” “O Ghaffâr, forgive me.”
Allah says: “And Allah has the most beautiful of names, so call to Him by them.”
As for the practice of repeating a name 100 times after `Asr and other similar practices, there is no basis for this whatsoever.
And Allah knows best.
Source: Islam Today