In order to correctly avoid evil eye we should strive to use the recommended invocations from the Quran and the Sunnah. One should say “Barak Allaahu ‘Alayk” (بارك الله لك أو عليك) which means “May Allaah’s blessing be upon you” to avoid evil eye, not “Maa Shaa’ Allaah” (ما شاء الله) which means “What Allaah wills.” The evidence for this is as follows ;
‘Once a man praised another man for having very beautiful skin and claimed he had never even seen a virgin with such beautiful skin.
The man became ill on the spot, and upon hearing about this, the Prophet ﷺ asked: “Why did you not say, May Allaah bless you?”’
[Muwaṭṭā of Imām Mālik (No. 1972, 1973) and it is Ṣaḥīḥ]
The Prophet ﷺ said: When one of you sees in a person something which amazes him, then let him supplicate (to Allaah) to bless him.”
[Jāmī’ Mu‘mār (No. 19766) and it is Ṣaḥīḥ]
Evidence against using just Maa Shaa’ Allaah: The Prophet ﷺ is reported to have said: “Whoever sees something that amazes him, let him say: “Maa shaa’ Allaah, Laa Quwwata illaa billaah” Hence, by doing so that person won’t be affected by the evil eye.”
[Ibn Sunni in “`Amal yaum wal-lail” (207)
In conclusion : If you think you have given someone evil eye, say “Allaahumma baarik ‘alaih” (اللهم بارك عليه) which means “O’ Allaah send your blessings upon him.”
[Ibn al-Qayyim’s Zaad al-Ma’aad (v. 4, p. 157-158)]