A senior advanced disciple wrote,

1. I was ill and not praying tahajjud. During that period two guests came to stay. They got up for tahajjud.

2. I thought to get up and pray, however another thought came not to do so as it  will be ostentatious. Eventually I didn’t pray. 

3. I thought of letting them know later that there was a reason for not offering tahajjud. 

Hakim al Ummah Maulana Ashraf Ali Thanvi (Allah have mercy on him) replied,

‘1.  This was the most appropriate ruling (in those circumstances)

2. This would had been the most appropriate action (i.e. to pray)

3.  This was pure ostentation (riya)

Imperfect individuals (like us) are instructed to act and correct the intention. Otherwise, they will find an excuse of possibility of riya in all matters (and abandon them). ‘

Al Qawl al Jaleel, page 55